186 



MUSEUM OF ANIMATED NATURE. 



[Ammonites. 



nrithin which we perceived the siphon with iu open 

 extremity : while the other four arms were disposed, 

 two on the right, and two on the lel^, in the middle 

 part of the ooening of the shell, contracted and bent 

 irregularly back. As to the higher arms, their dis- 

 position was altogether different from that of the 

 others. Prolongmg themselves towards the re- 

 treating part of the spire, one on each side, they en- 

 countered the keel by the tangent line ; and then, 

 without quitting if, stretched out as far as its an- 

 terior extremity, insinuating themselves between 

 the tubercles, and in such a manner, that there 

 remained in the medium line of the keel only a 

 narrow space that was not covered. The mem- 

 branous portion of these arms dilated beyond any 

 thing we could have pictured to ourselves from a 

 knowledge merely of the animal preserved in spirits 

 of wine, and was spread over the two lateral sur- 

 faces of the shell, in such a manner as to cover it 

 completely from the extremity of the spire to the 

 edge of the opening, and consequently of the keel. 

 The application of these membranes was direct and 

 without any puckerings or irregularity whatever ; 

 the lower part of the two large arms being com- 

 pletely stretched formed a kind of bridge over the 

 cavity left between the back of the poulp and the 

 retreating portion of the spire, in which the e.\- 

 tremity of a cluster of eggs was floating." Some- 

 times, however, the arms are somewhat retracted, 

 drawing back the expansion, and leaving the anterior 

 portion of the shell uncovered. In this condition 

 It is represented at Fig. 2533, which represents the 

 animal contracted within its shell, peeping above 

 iu ed^e, and with the limbs folded down. The eggs 

 are distinctly seen under the bridge made by the 

 velated arms. 



"To return to the description of our poulp," says 

 M. Rang, "which we left contracted within the 

 ^rgonaut-shell, and watching with an attentive eye 

 what took place around it, we saw it extending 

 itself from out its shell, and protruding six of its 

 arms; then it threw itself into violent motion, and 

 travelled over the basin in all directions, often 

 dashing itself against the sides. In these different 

 movements the body leant a little towards the an- 

 terior part of the shell ; and the long slender arms, 

 very much extended and collected into a close 

 bundle, were carried before it, as well as the tube, 

 which showed itself open and protruded. The 

 locomotion was eiFected in the ordinary manner of 

 poulps, the movement being backwards by means 

 of the contraction of the sac and the expulsion of 

 water through the siphon*. The disposition of the 

 animal and shell is the most favourable for accele- 

 rating tlie motion of the creature. The lightness of 

 the shell, — its narrow and keeled form, — its width, 

 which is smallest at the part presented first for 

 cleaving the water, — the membrane smoothing over 

 all inequalities of the shell, — the bundle of arms ex- 

 tending behind so as to offer the least possible re- 

 sistance, — the two arms stretched like a bridge over 

 the cavity where the eggs are, as if to throw off the 

 water from that cavity ; — all these adaptations con- 

 cur to facilitate the gliding of the animal through 

 the medium in which it is to move." 



M. Rang thought that he perceived in the move- 

 ments of the animal, when in open water, that it 

 had its back uppermost, and consequently the tube 

 below ; but he did not constantly see it so ; he ob- 

 served it however with more certainty in specimens 

 of poulps whose arms had been deprived of their 

 membranes. 



The animal which they had been watching, as 

 above described, fatigued by its efforts in a confined 

 space, and perhaps injured by the shocks which it 

 had sustained in coming in contact with the side of 

 the basin, allowed itself to sink to the bottom, and 

 half contracted itself in order to take repose ; soon 

 after which it exhibited another and unexpected 

 spectacle. Fixing some of the acetabula, or suckers, 

 of its fore-arms upon the bottom of the basin, it 

 erected itself straight upon its head, spreading out 

 its disc, and carrying the shell above it in the 

 ordinary manner of shelled gasteropods (snails) ; 

 then beginning to crawl, it presented tne appearance 

 of a pectinibranchiate mollusk. Half drawn back 

 into its shell, the animal appeared to crawl upon 

 its disc, the palmatures of which were a little raised, 

 to follow the movements of its arms ; the body was 

 hidden in the shell, the siphon placed in the an- 

 terior part of it was turned forwards, the arms, 

 which were at liberty, were very much protruded, 

 and twisting round, two before, and two on each 

 side ; the base of the two large velated arras seemed 

 to prolong the locomotive surface backwards, and 

 then, rising along the keel, they covered it with 

 their large membranes as when the poulp was 

 swimming in deep water. " Thus," continues M. 

 Rang," this mollusk, at once pelagic and littoral, 

 presents a most singular anomaly, when it swims at 

 the surface of the water having its ventral part 

 lowermost, and when it crawls along the bottom 

 having it, on the contrary, uppermost ; two things, 



which are completely contrary to what we see 

 among the marine mollusks on the one hand, and 

 the littoral mollusks on the other." Fig. 2534 

 represents the Argonaut moving on its head at the 

 bottom. 



Fig- 2535 represents the position of the animal 

 while propelling itself through the water in the act 

 uf swimming. The arrow indicates the direction 

 of the animal ; the siphon, throwing out succes- 

 sive gushes of water, is seen under the extended 

 arms. 



While crawling along the progress made was slow, 

 and it seemed to work its way like a snail, but this 

 motion was only apparently reptant, for the suckers 

 were the organs of loniomotion. 



When the poulp was at the point of death, it 

 drew in by slow degrees its large arms and their 

 membranes, and contracted them upon themselves 

 and all the othtr arms, so as to obstruct the opening 

 of the shell. At this moment the shell was moved, 

 and the poulp separated itself from it, not volun- 

 tarily but accidenlallj~, for it no longer held it in 

 any way. It appeared at first to become a little re- 

 animated, made some movements in the basin upon 

 its head, then tell from weakness, and soon died. 

 All this passed in less than ten minutes. 



Another form of shelled cephalopod is presented 

 to us in the Spirula. The shell is concealed under 

 the mantle at the lower part of the body, and is 

 spiral, but the whorls are separated from each other 

 instead of being contiguous ; internally it is divided 

 into chambers prelorated by a siphon, and the last 

 or external turn of the spire is prolonged in a straight 

 line. Our information respecting the Spirula is very 

 limited. 



In the Ammonites, Belemnites, &c., we are pre- 

 sented with the fossil relics in great abundance of 

 extinct testaceous cephalopods ; and certain distinct 

 forms of them are characteristic of certain systems 

 of rocks. According to Dr. Buckland the family of 

 the Ammonites* extends through the entire series 

 of the fossiliferous formations from the transition 

 strata to the chalk inclusive. Cuvier appeared to 

 consider the Ammonites as internal shells, like 

 Spirula; and found one reason in the smallness 

 of the outer chamber of lodgement ; but in the 

 opinion of Professors Owen and Buckland, they 

 were external shells, in the outer chamber of which 

 the animal resided. The latter thus writes ; — ^" The 

 smallness of the outer chamber or place of lodgement 

 for the animal is advanced by Cuvier in favour of 

 his opinion that Ammonites, like the Spirula, were 

 internal shells. This reason is probably founded on 

 observations made upon imperfect specimens. The 

 outer chamber of the Ammonites is very seldom 

 preserved in a perfect state ; but when this happens, 

 it is found to bear at least as large a proportion to 

 the chambered part of the shell, as the outer cell of 

 the Nautilus Pompilius bears to the chambered in- 

 terior of that shell. It often occupies more than 

 half, and in some cases the whole circumference, of 

 the outer whorl. This open chamber is not thin 

 and feeble like the long anterior chamber of the 

 Spirula, which is placed within the body of the 

 animal, producing this shell, but is nearly of equal 

 thickness with the close chambers of the Am- 

 monite." 



Fig. 2536 represents a Section of Ammonites 

 obtusus ; a, b, c, d, the outer chamber ; the siphon 

 or tube of communication may be traced from d, 

 where it opens into the last or outer chamber, along 

 the edge of the section, e,f, g, h, i, to the very nu- 

 cleus of the shell ; the waved transverse lines repre- 

 sent the partitions of the chambere. 



In some species the margin of the outer chamber 

 is reflected and thickened, in some it is prolonged 

 into a beak ; some species are furnished with spines, 

 others are rugose. 



Fig. 2537 represents the Beaked Ammonite (A. 

 rostratus). Figs. 25.38, 2539, 2540, 2541 (a, rim of 

 mouth), 2542, 2543, and 2544, exhibit various species 

 of Ammonites, with perfect mouths, the outlines of 

 which may be compared. 



Figs. 2545 and 2.546 exhibit other specimens of 

 perfect-mouthed ammonites (a, outline of the mouth 

 of Fig. 2546), and Fig. 2547, the Ammonites nodosus, 

 which will convey an idea of the concamerations in 

 some of the species. Fig. 2548 represents an 

 ammonite with an imperfect mouth, and Fig. 2549 

 a section. 



As the ammonites, of which about two hundred 

 and twenty-three species are distinguished, were 

 evidently principal agents for keeping within bounds 

 the mollusks, &c., the crustaceans, and perhaps 

 fishes of the periods prior to the chalk formation, 

 and belonging to the latter epoch, we should ex- 

 pect to find them widely distributed. Accordingly, 

 they occur in Europe, Asia, and America, in strata 

 apparently of the same date. In some instances, 

 the genera and even the species are identical. Dr. 

 Gerard found in the Himalaya Mountains, at an ele. 



* Fonnerly called Corntia Ammonii, Uonu of Jupiter Antmon, 

 whence the modern term Ammonite. 



vation of sixteen thousand feet. Ammonites Walcotii 

 and Ammonites communis, fossils that are found in 

 the lias of Lyme Regis. M. Mdnard met with one 

 in the Maritime Alps at an elevation of one thou- 

 sand five hundred toises. Their numbers must have 

 been great : M. Dufresne informed Lamarck that the 

 road from Auxerre to Avalon in Burgundy was 

 absolutely paved with them. The individual 

 agency too of some of these carnivorous instruments 

 for preserving the balance of marine animal power 

 must have been of no small importance. Lamarck 

 says that he has seen ammonites of two feet (French) 

 in diameter. Mr. James Sowerby and Mr. Mantell 

 record ammonites in the chalk with a diameter of 

 three feet; and Dr. Buckland states that Sir T. 

 Harvey and Mr Keith measured ammonites in the 

 chalk near .Margate which exceeded four feet in 

 diameter ; and this in cases where the diameter could 

 have been in a very small degree enlarged by 

 pressure. 



Dr. Buckland is of opinion that the Rhyncholites, 

 or beakstones, which occur so abundantly in the 

 oolite of Stonesfield, in the lias at Lyme Regis and 

 Bath, in the muschelkalk of Luneville, &c., were 

 the mandibles of ammonites as well as of fossil 

 nautili, and there can be no reasonable doubt of 

 the fact. 



It would appear that the ammonites, or rather 

 the cephalopods inhabiting these shells, had no ink- 

 bags ; but for much information on this and other 

 points we refer to Dr. Buckland's Bridgewater 

 Treatise, in which their history is copiously 

 illustrated. 



2550. — Duval's Crioceratitk 



(Crioceratiles Duvallii). This fossil shell is closely 

 allied to the Ammonites, but the whorls are apart and 

 not contiguous as in the latter. This form has 

 received from Mr. Sowerby the generic title of 

 Tropaeum. 



We may now pass to a group of the shells of 

 extinct cephalopods, termed Goniatites, a group of 

 equal importance with the ammonites, in reasoning 

 on the succession of organic life on the globe. 

 Between these shells and the ammonites there 

 are important distinctions. In the ammonites the 

 siphon, as we have seen, instead of perforating 

 the disc or centre of the transverse plates dividing 

 the chambers (as in nautilus), touches and runs 

 parallel to the inner surface of the shell on the 

 dorsal line. Another characteristic of the ammon- 

 ites is in the form of the sutures or intersections of 

 the transverse internal septa, or plates, with the 

 inner surface of the shell ; these sutures in ammon- 

 ites are undulated or angularly bent into lobes and 

 sinuses, seldom zigzag : in nautilus they are even, 

 or gently waved, but in goniatites the forms of the 

 sutures are in general singularly waved, zigzag, and 

 greatly varied. Von Buch regards the sinuous 

 edges of the septa of the ammonites and goniatites 

 to be necessarily derived from the doi-sal position 

 of the siphuncle ; " all the other differences," he 

 says, "are derived from this primary distinction. 

 The nautilus, which passes a very large siphon 

 through the middle of the septa, appears sufficiently 

 attached by this membranous basis on which it 

 rests. There is no need of any other support, and 

 the septa in general" remains smooth, and concave 

 without sinuosities on the edges. The small dorsal 

 siphon of the ammonites (and goniatites, which 

 Von Buch regarded as included in that group) 

 would not suffice to secure the animal from dis- 

 placement on the surface of its cell." He contends 

 that other supports^are needed, and that they are to 

 be found in the marginal lobes, which the form of 

 the goniatites, in particular, impresses on the parti- 

 tions of the chambers, and which are generally six 

 in number, as seen at Fig. 2551. One ventral, V; 

 one dorsal, D ; and two on each side, L L, L' L'. 



The species of Goniatite are rather numerous : the 

 late Mr. Martin, in his 'Petrificata Derbiensia,' 

 figured two species from the limestone ; Mr. 

 Sowerby, in the 'Mineral Conchology of Great 

 Britain,' added two others ; and Professor Phillips, in 

 the ' Illustration of the Geology of Yorkshire,' has 

 raised the number of British species to thirty-six; 

 of these the septa are completely ascertained. 

 These, added to the distinct continental species, 

 make up a total of seventy-one or seventy-two with 

 which naturalists are acquainted. 



With respect to their external form, the goniatites 

 form a sub-globular figure, to the discoid spiral 

 shape of the flattest ammonites. Most have 

 rounded backs, a few have the back carinated. In 

 general the lines of growth externally visible are 

 sigmoidally waved; sometimes, however, the striae 

 are annular, sometimes radiating; occasionlly the 

 strise rise into tubercles on the inner edge of the 

 whorls. 



2552. — The Truncate Goniatite 



(Goniatites tfuncattis). In this species the striae arc 

 sigmoid. 



