Spondylid^.J 



MUSEUM OF ANIMATED NATURE. 



259 



The fossil species of the genus Ostrea are very 

 numerous; they occur as low iu the series of strata 

 as the lias limestone, inclusive : M. Deshayes, in his 

 last edition of Lamarck, gives the number as 

 eighty-two. 



From the genus Ostrea we advance to the genus 

 Piacuna, of which those large diaphanous and 

 almost circular shells to be observed in most col- 

 lections are examples. 



The genus Piacuna presents the following cha- 

 racters: — The shell, which is very much flattened, 

 is of a regular figure, and not adherent to other 

 bodies. The valves are almost translucid, quite so 

 in some species, and nearly equal ; the hinge is 

 internal, and offers on one valve two lon>;itudinal 

 rib-like elevations converging at the summit, and 

 on the other two corresponding furrows for the 

 attachment of the ligament. The muscular im- 

 pression is nearly centrical and rather small. 



The mollusk does not appear to be known. Three 

 living species are recorded, and one fossil, in ter- 

 tiary deposits. 



The living species inhabit the Indian and Red 

 Sea^. 



2879. — The Chinese-Window Oyster 



(Piacuna Placenta). The valves of this shell are 

 sufficiently transparent to admit light; they are 

 suborbicular, flat, and white, with longitudinal 

 decussate striiF. It inhabits the Indian Seas, and 

 is taken on sandy bottoms. 



In the 'Proceeds. Zool. Soc' for 1832, p. 28, 

 Mr. Bro'.lcrip characterizes a genus which he terms 

 Placunanomia, forming, as its name indicates, an 

 intermediate link between Piacuna and Anomia. 

 The generic characters are detailed as follows: — 



Shell adherent, subequivalve, irregular, flattened, 

 plaited towards the margin, vitreous internally. 

 Hinge internal, with two elongated, thick, sub- 

 curved, divaricated teeth converging at the base in 

 the lower valve, and two ligamentiferous furrows 

 opposite in the upper valve. Lower valve super- 

 ficially fissured externally towards the hinge, the 

 siibosseous organ of adhesion inserted between the 

 laminae of the shell and filling the fissure exter- 

 nally. Muscular impression in each valve sub- 

 central. In the upper valve the impression of the 

 organ of adhesion is superadded. (Uroderip.) 



The learned founder of the genus follows up these 

 characters, with the annexed observations : — 



" This interesting genus partakes of the characters 

 of the genera Ostrea, Plicatula, Piacuna, and 

 ■ Anomia. It may be regarded as the connecting 

 link between the two latter. With an arrangement 

 of the hinge approaching very nearly to that of 

 Piacuna, it has the distinguishing organization of 

 Anomia, while the external appearance of the shell, 

 especially if viewed in situ, bears the strongest 

 resemblance to Plicatula or some of the plicated 

 oysters. The organ of adhesion, which in its bony 

 character (for it is more bony than shelly) resembles 

 that of Anomia, does not perforate the lower valve 

 directly, but is inserted between the laminae of the 

 internal surface of the lower valve, above the mus- 

 cular impression and below the hinge, and passes out 

 into an external, irregular, somewhat longitudinal 

 superficial fissure or cicatrix, which is narrowest at 

 the hinge margin, and which it entirely fills to a 

 level with the surrounding surface of the shell." 

 (Broderip, ' Zool. Proc' February, 1832.) 



The PlacunanomiiE appear to be widely distri- 

 buted ; they inhabit the seas of warm climates in 

 both hemispheres. Mr. Broderip has described four 

 (' Zool. Proc' and Miiller's 'Synopsis') brought to 

 this country by Mr. Cuming, from the West Indies, 

 Central America, and other western localities. 

 They were dredged from sandy mud and muddy 

 bottoms, adhering to bivalve shells, dead and living, 

 and dead coral, at depths of six, eleven, and seven- 

 teen fathoms ; of these, Piacuna echinata wears 

 something of the appearance of the shoit-spined 

 Spondyii. Besides the species above alluded to, 

 Mr. Broderip slates that Mr. Sowerby furnished him 

 with an odd valve of a large species from Luconia, 

 which was beautifully iridescent internally; but 

 as it was believed that this was identical with the 

 fine shell sold by him to the British Museum, Mr. 

 Broderip left the des;'.ription of it to the ofiicers of 

 that establishment. Mr. Sowerby had some other 

 odd valves, which Mr. Broderip thought might 

 prove new, and the latter possessed two or three 

 specimens adhering to Spondyl'i, from an unknown ji 

 locality; but they appeared to be young, and j 

 though he was inclined to think that there was a I 

 new species among them, he deemed it prudent to 

 wait lor further information. 



M. Deshayes remarks that this genus establishes 

 the passage between Piacuna and Anomia, and 

 that it shows that the V-shaped tooth of Piacuna 

 is only an extreme modification of the large callosity 

 of the Anomiae ; he adds that a fossil shell found in 

 ^S)P'' ^nfJ which has been taken for a Piacuna, 

 Vol II. 



is a new step, as regards the hinge, between the 

 Anomiae and Piacunie. 



2880. — Cuming's Placunanomia 

 (Plactmanomia Ciimiiujil, Broder.). In this species 

 the shell is somewhat rounded, and the margin is 

 plaited ; the figure flattened ; the general colour is 

 white obscurely silvered. Length two and a half 



[ers. 

 America 



Inches ; height two inches and three-tju«|( 

 It is ^lative of JLlie shores of CemRH 

 (the GulW)f Dulce, province of Costa Rica), and was 



dredged up by Mr. Cuming at the depth of eleven 

 fathoms, attached to dead bivalve^Bfclls and dead 

 coral. 



Referring to Fig. 2880, a exhibits the internal 

 appearance of the organ of adhesion ; h, the same 

 seen externally. 



We now turn to the genus Anomia. 

 In this genus the mollusk is very compressed in 

 form, and has the edges of the delicate mantle 

 fringed with a row of tentacular filaments. The foot 

 is rudimentary. The adductor muscle is divided 

 into three branches, and the largest of these passes 

 hy a notch in the lower valy*, a n^-b ecomes attached 

 to an opercular stony or corn^fl^ piece, which is 

 fixed to marine substances, as ^ffk or dead shells ; 

 in this singular manner is the anomia moored. 



The shell thus attached by its opercular piece, is 

 inequivalve, irregular in outline, delicate, and olten 

 translucent. The fixed valve is the most flattened, 

 having a round or oblong notch near the umbo, 

 through which passes the muscular slip crowned 

 with its opercular apex; the other valve is larger 

 and more convex. The hinge-ligament is short and 

 : thick. The muscular impression is divided into 

 ikthree portions. 



^ The Anomiae occur in the European seas and the 

 ;; Atlantic ocean : M. Deshayes in his tables records 

 ji ten living species — eight species in tertiary forma- 

 tions, and two species found both in a recent and 

 fossil state. It, is one of the latter that we select 

 for our example. 



2881. — TuE Saddle .\nomia 

 {Anomia Ephippium). This species is of large size ; 

 it is found in the British Channel, the Mediterra- 

 nean, and the Atlantic Ocean, a represents the 

 shell with the valves closed ; b, the shell open to 

 show the hinge ; c, the hinge of the attached valve 

 without the bony appendage. 



Fig. 2882 shows the bony appendage of Anomia 

 Ephippium : a, the bony part that goes through the 

 opening of the shell ; h, the surface which is at- 

 tached to external objects. 



Fig. 2883 represents a species termed by M. de 

 Blainville Anomia squamata, which has not this ad- 

 ditional bony appendage, and which he says is at- 

 tached to objects by the valve itself. Mr. Sowerby 

 supposes it to be the Anomia Ephippium in a very 

 young state, before the appendage is ossified. 



Family SPONDYLID.E (SPINY OYSTERS, 

 WATER-CLAM, &c.). 

 According to M. Deshayes, the family Spondylidae 

 contains two genera, viz., Spondylus, into which he 

 merges Podopsis, Dianchora, and Pachytes ; and 

 Plicatula, which indeed stands only on uncertain 

 grounds, agreeing with Spondylus in all essential 

 characteristics. In the Spondyii there are auricles, 

 or angular processes, on each side of the hinge ; and 

 the umbo of the great valve is produced into a pro- 

 jection having a flattened surface divided by a fur- 

 row in which the old traces of the ligament may be 

 perceived : on the contrary, in Plicatula the auiicles 

 rarely exist, and where they appear, are small, and 

 there is no projection (talon) of the umbo ; yet do 

 the two genera merge insensibly into each other, 

 for in some species of Spondylus the talon is trifling 

 and without furrow, and the ligament is entirely 

 concealed, as in Plicatula; while, per contra, in 

 some species of Plicatula there i^n approximation 

 in the development of the umbo to that of Spondy- 

 lus. Plicatula must in fact be regarded only as a 

 convenient subgenus of Spondylus 



In the genus Spondylus the characters may be 

 summed up as follows: ^ 



Shell unequivalve, adhering fo external obje«||^ 

 auriculated, beset with spines or rough ; the um- 

 bones unequal ; the lower valve offers an external 

 cardinal (caido, ahinge) facet, which is flattened and 

 divided by a furrow, and which increases with age. | 

 Hinge furnished with two strong teeth in each valve, i 

 with an intermediate fosset for the ligament, com- ! 

 municated by its base with the external furrow. The 

 ligament is external, and its old and useless re- 

 mains show themselves externally in the furrow. j 



The mollusk is rounded or oval, its thickness ! 

 varying in the different species. The two lobes or ' 

 laminae of the mantle are disunited at their edges, ' 

 excepting along the short extent of the dorsal bor- 

 der corresponding to the hinge; their margin is , 

 thick and furnished with several rows of long fleshy ' 

 cilia, between which and on the internal border i 



may be observed a certain number of cilia at irre- 

 gular distances, truncated as it were in the middle, 

 and terminated by a smooth, convex, coloured sur- 

 face, calling to mind the ocular surface of the ten- 

 tacles in the snail. The branchiae resemble those 

 of the Pectens. The adductor muscle is large and 

 circular. The mouth is situated at the anterior 

 commissure of the mantle, and surrounded with a 

 large slashed lip, fringed on the edge and accom- 

 panied on each side by a pair of palps, but little 

 elongated, in the form of myrtle-leaves. 



At the anterior ])ait of the animal is seated a pe- 

 culiar orj^an : it consists of a disc supported by a 

 short pedicle ; from the centre of this disc emerges 

 a cylindrical tendon, terminated bya small, oviform, 

 fleshy mass. This is evidently a modification of the 

 foot, which, as it is not needed in the fixed Spondy- 

 lus as a locomotive organ for the purpose of chang- 

 ing the place of the animal, is probably rendered 

 subservient to the direction of the ciliaiy currents 

 charged with food to the mouth. 



Cuvier says the Spondyii are eaten like oyster* ; 

 their shells are often tinged with lively colours. 

 They are inhabitants of the Mediterranean and the 

 warmer seas, and are found attached to corals, 

 rocks, dead shells, &c., at depths varying from the 

 surface to seventeen fathoms. Several splendid 

 species are natives of the intertropics. An eminent 

 conchologist, whose means of observation have been 

 very extensive, makes the following interesting re- 

 marks : he says, every one must have noticed the 

 spines with v^■hich the Spondyii are armed, and 

 which in some instances are very long, bristling out 

 on every side from the upper valve. "The lower 

 valve is attached and adheres to submerged bodies 

 by means of foliations. If the whole lower surface 

 adheres, as it often does, not a spine is given out 

 from the lower valve ; but where the adhesion takes 

 effect towards the anterior part of the lower valve 

 only, as is frequently the case, especially when the 

 shell is affixed among the branches of corals, a fa- 

 vourite locality with some species, the foliations are 

 confined merely to that part where adhesion is re- 

 quired, and the rest or free pait of the valve is as 

 profuse of spines as the upper valve itself. There 

 are two points to be gained— support or adhesion, 

 and defence. The first is of primary importance; and 

 as soon as that is siife, all the resources of the animal 

 seemed to be turned towards the offensive and de- 

 fensive armour. Those fishes which browse among 

 the corals are thus deterred from injuring the living 

 fixture which has there taken up its abode. A very 

 fine series of specimens was collected with a view 

 to this habit, and they sliowed not only the power 

 which the animal had, of secreting the proper pro- 

 cess of shell, according to the circumstances re- 

 quired, but of modifying the secretion according to 

 the exigencies of the occasion." 



2884. — The Ducal Spoxdti.us 

 {Spondi/liis ducalis). In this example of the present 

 genus the internal surface of the valve is dis- 

 played, showing the hinge, ligament, muscular im- 

 pression, &c. : a, the upjicr valve ; b, the lower. 



2885. — The American Spondylls, or 



SPINV OvSThR 



{Spondylus Americamis) . In this example the 

 valves are closed, with tlie umbones towards the 

 spectator. 



Fig. 2886 represents a section of the large spon- 

 dylus, or Waterclam (Spondylus varius, Brod.), the 

 valves of which are remarkable for the nacreous 

 layers forming a series of hollow chambers or 

 reservoirs, filled, many of them, with fluid. In 

 young shells these chambers are not formed, but 

 only in those of an advanced period of growth. 

 The water can not only be heard trickling as the 

 position of the shell is changed, but distinctly seen 

 through the last transparent nacreous layer, foiming 

 the immediate bed of the mollusk. 



On this camerated structure a valuable paper by 

 Professor Owen, will be found in the "Proceeds. 

 Zool. Soc' 1837, p. 63, et seq. The following is 

 part of that communication : — 



" In order to examine this camerated structure, 

 and more especially to see how it was modified by 

 the presence and progressive change of place of the 

 adductor muscle, I had a fine specimen sawn through 

 vertically and lengthwise. The specimen in question 

 measures eight inches in length ; and the substance 

 of the concave valve, which is two inches one-third 

 in thickness at the thickest part, includes fourteen 

 chambers, separated from each other by very regu- 

 larly formed and stout partitions, composed, as in 

 other chambered shells, of the nacreous portion or 

 constituent of the shell. The septa (or divisions) 

 are slightly undulating in their course, but present 

 a gradual concavity towards the outlet of the shell. 

 Not any of these partitions, however, are continued 

 freely across the shell ; — but each becomes con- 

 tinuous at the muscular impression, which is near 

 the middle of the shell, willi the contiguous septa, 



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