Chitons.] 



MUSEUM OF ANIMATED NATURE. 



251 



Fig. 2846 represents the animal extricated from 

 the shell, in different views: D, the animal magnified, 

 the abdominal aspect ; a. the extremity of the foot ; | 

 b, the collar of the mantle ; d d, the liver ; e, the in- 

 testinal lube ; /, the efrg-sack : g, the muscle of in- 

 sertion ; j and h, the expanded expansion, which is 

 fimnel-shaped, and called by Deshayesthe pavilion ; 

 I egpstive orifice ; F, the same, dorsal aspect, mag- 

 nified ; a. extremity of the foot; b, the collar; c c, 

 the month : d. a slight projection produced by the 

 head and the branchia; ; e c, internal retractile mus- 

 cles; //, external retractile muscles; jr, the neck 

 of the pavilion ; h, the pavilion ; e, the same, with 

 the mantle slit along the dorsal and medial line, de- 

 tached in part from its posterior insertion, and turned 

 aside, so as to show the parts enclosed ; a, the ex- 

 tremity of the foot, which closes the aperture, j, of the 

 collar, I VI, of the mantle, n op; b b, lobes of the 

 foot ; r, the foot itself, presenting a depression, or a 

 channel, running its whole length; rf, the head ; e, 

 the cerebral ganglion ; //, the two jaws; g g, the 

 peduncles of the branchite ; hh, ii, the branchiae; 

 pp, g g, the retractor muscles ; s, the muscle of in- 

 sertion ; /, the pavilion ; o, the animal, one-fourth 

 of natural size ; h, the same, one-sixth of natural 

 size. 



The genus Dentalium is very widely distributed, 

 few seas being destitute of some species. Generally 

 these shells are found on sandy shores, in rather 

 shallow water, but sometimes at consideral)le depth. 

 The species, as enumerated by Deshayes, are twenty- 

 three living, and thirty-four fossil in beds of tertiaiy 

 formation. Four new species, from the shores of 

 South America, w ill be found described by Mr. G. B. 

 Sowerby in the ' Proceedings of the Zoological So- 

 ciety,' ls.3-.', p. 29. 



Family CHITONID^ (CHITONS ; Les Oscabrions 

 of the French). 



The Chitons constitute a very remarkable group of 

 mollusks, covered by a shell formed of eight distmct 

 portions, arranged upon the back, in a single row, 

 and attached to a tough leathery mantle, the edges 

 of which extend beyond the borders of the plates ; 

 these latter are transverse, and overlap each other, 

 constituting a sort of armour, veiy different, indeed, 

 to the turbinated shell of most groups, or the coni- 

 cal shell of a limpet ; they are differently marked 

 and patterned in different species, and the border is 

 mostly covered with scales, hairs, or spines. Thus 

 protected, the Chiton can roll itself up like an arma- 

 dillo, and stretch itself out again for the purpose of 

 progression, or of attaching itself, limpet-like, to the 

 rock. This power supposes an arrangement of mus- 

 cles in connexion with the plates, in order that the 

 mechanism of the armour may be complete. The 

 foot of the mollusk is oval, and the branchiae con- 

 sist of small leaflets placed, as in Patella, in the fur- 

 row between the foot and the mantle. They are 

 covered with cilia. 



There is no projecting distinct head, and both eyes 

 and tentacula are wanting. The mouth is furnished 

 with a long tongue, rolled up spirally, and armed 

 with horny teeth. 



Fig. 2847 represents the eight shelly plates of 

 Chiton, separated from the mantle, and from each 

 other, so as to show their outline. 



Fig. 2848 shows the shelly plates of an allied ge- 

 nus termed Chitonellus. 



Fig. 2S49 shows the animal of Chiton squamosus; 

 o, the animal and shell seen from above ; b, the ani- 

 mal seen from below ; c, a side view of the shell and 

 animal in a creeping or adherent state ; d, a portion 

 of Ihe branchiaa magnified. 



Though the Chiton has no affinity to the multi- 

 valve shells of Linnaeus (the Lepas and Balanus, or 

 barnacles), yet they were all associated together by 

 that naturalist, forming an artificial group compo.sed 

 of a most heterogeneous assemblage ; and though 

 his arrangement has been long abandoned (Adan.ion 

 having, indeed, demonstrated the true characters of 

 the animal by careful observations, and Cuvier hav- 

 ing confirmed Adan.son's views by anatomical inves- 

 tigation), yet M. de Blainville has, in some measure, 

 returned to the linn-jean arrangement, and formed 

 a section of the mollusca, termed Malentoioaria, of 

 which Lepas and Chiton form two classes. This ar- 

 rangement, however, has not been adopted by other 

 zoologists, who generally recognise the affinity of 

 Chiton to Lepas. 



The Chitons are specifically veiy numerous, and 

 are found on mo^t rocky shores; they attain to the 

 largest size in the iiotter climates, with some excep- 

 tions, for two large species occur on the shores of 

 Tierra del Fuego ; none, however, appear to exist in 

 the high northern seas, and the British species are 

 small. We may now turn to our pictorial speci- 

 men.s, of which such are selected as illustrate the 

 minor groups into which the gonus is for conveni- 

 ence divided. 



Section a. In the species of this section the bor- 

 der of the mantle is leathery and naked.. The fol- 

 lowing t.vo species arj examples. 

 Vol. U. 



2850. — The Chilian Chitok 



(Chiton chilcnsis). This Chiton has the shell ob- 

 long-ovate, opaque, and thick, of a dark-brown co- 

 lour, smooth and dull ; the inside is white, with pink 

 markings on the first, second, and last plates. The 

 plates are marked by longitudinal striae, and crossed 

 by irregular concentric ridges. The anterior and 

 posterior plates are semilunate, and slightly punc- 

 tated; the second plate is subcarinated, with the 

 front margin obtusely angled, the lateral margins 

 arcuate ; and the posterior margin with a promi- 

 nent beak, on each side of whicli diverges a rather 

 elevated granulated ridge ; the next five valves are 

 alike bow-shaped, with a granulate ridge on each 

 side. The border is smooth, coriaceous, or leathery, 

 tough, thick, and of a darker colour than the shell ; 

 it is semipellucid, broad at the sides, and narrow an- 

 teriorly and posteriorly. 



This species of Chiton is found on the shores of 

 Valparaiso, in the crevices of rocks, and under stones. 



2851. — Dk Blainville's Chiton 



(Chiton Blainmllii). In this curious species the 

 border of the mantle is greatly enlarged anteriorly 

 and contracted posteriorly ; it is of an orange red, 

 and fringed here and there, not with hairs, but with 

 little coriaceous filaments. The shell is roundish, 

 the anterior plate is obscurely ranged, the posterior 

 one small and abrupt, the others are concentrically 

 lineated. The general colour is roseate, varied with 

 white, brown, and greenish ; inner surface white. 



This Chiton is found on the shores of the Inner 

 Lobos Island, coast of Peru. 



Section /3. In this section the mantle-border is 

 smooth, but with tufts of hair at the lateral extre- 

 mities of each plate. 



2852. — The Tufted Chiton 

 {Chiton fascicularis) . This is a small species found 

 on the southern coast of our island, and also in the 

 Mediterranean. Specimens from the Baibary coast 

 are stated by Montagu to measure not unfrequently 

 an inch in length. Bi itish specimens measure about 

 five-eighths of an inch in length, and rather more 

 than two-eighths of an inch in breadth. The shell is 

 apparently smooth, but, when examined by a glass, 

 presents a rough shagreened surface, except along 

 the elevated dorsal ridge ; around the margin, at 

 the junction of each plate, is a tuft of whitish hair ; 

 besides two tufts in front, making altogether eigh- 

 teen. The colour is brown or cinereous. 



Section y. In this section the mantle-border is 

 covered with hairs. 



2853. — The Peruvian Chiton 

 {Chiton Pemvianus). The Peruvian Chiton has 

 the border of the mantle narrow and coriaceous, and 

 thickly covered with long coarse black hairs. The 

 shell is oblong-ovate, opaque, of a dirty yellowish 

 green, or yellowish brown ; the inside is white. 

 The plates are thin and slightly elevated, having the 

 posterior compartments a little raised ; they are mi- 

 nutely striated. From between each emerges a se- 

 ries of short black hairs, which lie on the back of 

 the shell. 



This species of Chiton is found under stones at 

 low water, on the shores of Valparaiso Bay. Its 

 length is two inches, its breadth one inch and a half. 



Section S. In this section the mantle-border is 

 beset with spines. 



2854. — TuE SpiNOSE Chiton 

 (Chiton spinosus). In the Spinose Chiton the shell 

 is brownish black ; the plates are opaque, those an- 

 teriorly placed are granulated over the entire sur- 

 face, those posteriorly are granulated at the sides. 

 The border of the mantle is wide, and beset with 

 long aculeated blackish spines, closely resembling 

 those of certain Echini. Total length three inches. 

 This is a very rare species, and according to Peron 

 is a native of the South Seas. 



2855. — The SriNirEBOus Chiton 

 (Chiton spinipnus). Chiton aculeatus, Barnes, not 

 Linnaeus. 'J his is a large species, with the shell 

 opaque, oblong-ovate, reddish brown, and glossy; 

 the inside is reddish white. The posterior angles of 

 the plates do not overlap Ihe anterior edges of the 

 succeeding. The first plate has generally nine rows 

 of raised dots diverging from the apex, but the 

 number appears to vary with age ; the second plate 

 is rather acutely beaked and carinated, longer than 

 the five following, which are striated and shaped 

 alike, carinated, with an acute beak, and presenting 

 a row of elevated dots. The last plate is striated 

 and beaked, with a row of raised dots under the 

 beak. The border is coriaceous, thick, broad, rough, 

 and of a greenish or orange colour. In young spe- 

 cimens it is thickly covered with blunt spines, but 

 in old shells the spines are short and scanty, and 

 generally covered with corallines. 



This species attains to the length of five or six 

 inches, but it is then destitute of beauty, the sharp- 



ness of the pattern on the shell being lost, and the 

 spines covered with a dirty coat of calcareous mat- 

 ter, so often observed encrusting old shells and other 

 submarine bodies, the result of precipitation. 



Mr. Frembley, who found this species on the rocky 

 coasts of Valparaiso and Chili, states, that it fre- 

 quents exposed situations, and is olten Ibund adher- 

 ing to the rocks over which the sea breaks with great 

 violence, where there is no little danger as well as 

 difficulty in obtaining them ; they are generally co- 

 vered with sea-weed. 



Section i. This section is distinguished by the 

 border of the mantle being scaly. 



2866. — The Coquimbo Chiton 



(Chiton Coqnimhensis). The shell of this species 

 is ovate, narrow, and opaque ; — while young, its 

 colour is of a glossy greenish brown ; the inside 

 blackish. The anterior plate is marked with nume- 

 rous undulated concentric ridges, and all except the 

 first are rather acutely keeled ancl beaked ; a ridge 

 diverges on each side from the beak, forming a 

 sagittate figure, below which are longitudinal striae. 

 The border is thick, moderately broad, and co- 

 vered with coarse seed-like scales, which are at- 

 tached laterally. As the animal advances in age, 

 the middle of the plates, which are very solid, be- 

 come eroded, and covered with limpets, balani, &c. 

 The only locality, Mr. Frembley says, in which he 

 found this species, was on the south side of the coast 

 of Coquimbo bay. In its habits it resembles the 

 preceding species, excepting, as he states, that it 

 appears to be more gregarious. 



Section ?. In this group the border of the mantle 

 is granulous. 



2857. — The Magniwcent Chiton 



(Chiton magnificus). It is very difficult to give 

 by mere words an idea of the patterns which the 

 shells of the Chitons present, and of the form of the 

 separate plates. Mr. Frembley, whose details we 

 follow, characterizes the shell as dull, opaque oliva- 

 ceous, and dotted with lighter-coloured spots, with 

 the inside glaucous. The first plate has regularly 

 radiating striae crossed by concentric ridges; the 

 posterior margin is nearly straight. The other 

 plates are obtusely beaked, and divided laterally 

 into two compartments, the anterior having regular 

 longitudinal striae, crossed by others very minute 

 and concentric ; from under the beaks diverge to 

 the lateral margins of the plates coarse and more 

 irregular stria;, which raise the posterior compart- 

 ment above the other. The last plate has a w^li- 

 defined apex leaning towards the posterior margin. 

 The border is thin, moderately broad, and covered 

 with fine shining bead-like granulations of the same 

 colour as the shells. 



Ttiis species is the Chiton olivaceous of Frembley ; 

 but it had previously received from M. Deshayesthe 

 title of magnificus. It grows to the length of about 

 five inches ; and is found on the coast of Chili. We 

 now come to the genus or sub-gemis Chitonellus, 

 which contains such species as have the border 

 highly developed, and the valves very small ; in 

 some species, indeed, they are olten almost entirely 

 hidden under the skin of the mantle, so that the 

 animal has almost a naked appearance ; the body is 

 often almost vermiform. Fig. 2858 represents two 

 examples:— a, the smooth Chitonellus (Chitonellus 

 laevis) ; b, the larviform (Chitonellus larvaeformis). 



Whether the genus Chitonellus is founded on solid 

 grounds is very doubtful; a series of gradations 

 leads from the more completely armour-clad Chitons 

 to such as have the plates rudimentary and hid in 

 the mantle; and there is no point in Ihe series at 

 which a line of generic demarcation can be diawn. 

 Its retention may nevertheless be convenient. It 

 would seem that fossil species of Ihe Chiton are of 

 rare occurrence. We learn from Mr. Sowerby that 

 detached valves are occasionally found near Paris, 

 in the calcareous sand and in the crag of our island. 

 M. Deshayes, in his edition of Lamarck, gives one 

 species from the tertiary of Giignon, discovered by 

 M. Deli-ance, and a second species belonging to the 

 transition rocks in the neighbourhood of lournay, 

 due to the researches of M.VI. Duchastc] and Puzos. 



Here then we leave the Gastropodus mollusks ; 

 we have given a sketch of their principal Ibrms, 

 from the Slugs and Helices to the slug-like Chitons 

 covered with their shelly plates, not, we trust, with- 

 out having conveyed some degree of inlbrmation to 

 our general readers who wish to know more of these 

 animals than what may be learned from a mere ex- 

 amination of the shell. We now commence the 

 review of another class, namely, the Bivalve-shelled 

 Mollusks, or Acephalous Moliusks of Cuvier, the 

 latter term implying the absence of a distinct head. 



CLASS CONCHIFERA 



Bivalve -SHELLED Mollusks, or AcKrHALous- 

 SiiELi.ED Mollusks (Les Acej holes Testaces of Cu- 



