278 



MUSEUM OF ANIMATED NATURE. 



[Cythekka. 



2365.— The Varikgatbd A»«phidk»»i\ 

 ' Am/>l>!desma rariiyalum). The species described 

 l)V Limarck i« a native ol' the coast of Bnuil. 

 'With respect to the fossil species, five are re- 

 corded by Pliillips in the oolite group. Dr. Filton 

 des.-ribes and fiifiires one as doubtful, irom the 

 ureen-sand; and Mr. Lyell records another found 

 at Caltagirone. 



Closely aVIied fo Amphidesma is the genus Lu- 

 miniria. founded by Mr. G. B. Sowerby, and which 

 he says is remarkable for the dissimilarity of the 

 hinee of the two valves, one having a strong lateral 

 tooth on each vMve, the other being almost desti- 

 tute ol lateral teeth. •' Having:," says Mr. Sowerby, 

 " only met with a single West Indian species, I did 

 not venture to consider this genus established, until 

 Mr. Cuming showed me several species in his rich 

 collection of South American and Pacific shells, one 

 of which is sufRcientlv large to show the characters 

 distinctly.' (' Zool. Proceeds." 1838, p. 3i.) 



To this West Indian species must be added four 

 »pecies described in the above ' Proceeds." 1833, of 

 which one is the Cumingia mutiea. 



2966. — Thb Earless Cumingia 

 < Cuminf/ia muticn). Mr. Sowerby says that the 

 ligament of the hinge is internal in this genus, and 

 affixed to a somewhat ear-like pit or depression 

 (ligamento interno, fovcolte subcochlearilbrmi 

 affixo). The present species he describes as having 

 an oval shell, very minutely decussated, rounded 

 anteriorly, postcrioriy rather acute. It was ob- 

 tained at the following places: Conception, in seven 

 fathoms, on sand and mud ; at Iquiqui, in nine fa- 

 thoms, on gravel and mud ; at Payta, in hard clay 

 at low water ; and at Muerte. 



The other three species are C. lamellosa, from 

 Payta and Panama, C. coarctata, from the Bay of 

 Caracas ; and C. trigonularis, from St. Elena. No 

 fossil species as yet known. 



W'e now turn to the genus Mactra ; the distribu- 

 tion of which is very extensive, ranging through 

 the seas of Europe, the East and West Indies, Afri- 

 ca, North America, &c. 



The shell is transverse, inequilateral, subtrigonal, 

 sometimes a little gaping at the mdes ; the urabones 

 are protuberant ; the hinge has one cardinal tooth 

 in the form of the letter V, the point being nearest 

 the umbo, and the branches diverging from it ; close 

 to this is a very sharp thin tooth. Lateral teeth, two 

 on each side in one valve, one on each side in the 

 other. 



The moUusk is rather thick and oval; the bor- 

 ders of the mantle are simple, with two siphons, 

 but little elongated, and united. The foot is very 

 long and angular. 



The genus Mactra contains a very extensive se- 

 ries of species ; some of singular form, others re- 

 markable for beauty ; they mostly live on sandy 

 mud and sands, at depths varying from the surface 

 of the sea to ten or twelve fathoms. The living 

 species are about thirty in number. 



M. de Blainville divides them into the following 

 subgeneric groups : — 



1. Species whose cardinal teeth become nearly 

 obliterated, in consequence of the enlargement of 

 the ligamental depression. Example : Mactra gi- 

 gantea. 



2. Species all of whose teeth are very large, 

 lamellar, and not striated. Example : Mactra stul- 

 tonim. 



3. Thick and solid species without an epidermis ; 

 the lateral teeth finely striated ; the mantle pierced 

 with two openings, but almost without siphons. 

 Example : Mactra trigonella. 



4. Very thick, solid species, striated longitudi- 

 nally ; cardinal teeth none, or next to none ; lateral 

 teeth very thick, approximated, raised"; an external 

 ligament besides the internal one. Example : Mac- 

 tra crassa. 



2967. — ^The Brazilian? Mactra 



■(Mactra Brasiliana'). This species from Soulh 

 America may serve to represent the genus; it is 

 not rich in fossil species, which Mr. G. B. Sowerby 

 says are only to be found in tertiary beds, unless 

 some very singular fossils found in the secondary 

 strata, particularly the oolite, be truly referable to 

 this genus ; of this, however, we cannot be certain, 

 because we know not their hinges. They will be 

 found represented in Sowerby's ' Mineral Concho- 

 logy.' 



The genus Crassafella now presents itself. In 

 this genus the shell is equivalve, transverse, and 

 inequilateral. In one valve there are two strong 

 cuneiform, rugose, cardinal teeth, sometimes per- 

 pendicularly grooved ; in the other there is only one. 



The ligament is internal, and attached to a-oonvex 

 space placed on the anterior side of the hinge ; the 

 pit, however, is divided into two portiims, and that 

 part of the ligament attached to the outer portion 

 IS visible externally when the valves are closed. 



The muscular impressions are very distinct ; pallial 

 impressions simple, not sinuous. 



The species are found on the coasts of central and 

 South America, and in the seas of Australia. 



2968. — The Coumon Crassatella 



(Cratsatelia Kingicoia). We select this species as 

 a representative of the genus, which contains ten 

 or twelve recorded species, including two described 

 by Mr. G. B. Sowerby in the' Proceeds. Zool. Soc' 

 1.S32, p. 56, both from the shores of America, 

 where they were dredged up from sandy mud in 

 eleven fathoms of water. 



Fossil species occur in the calcaire grossier of 

 Paris, in the London clay, and, according to M. 

 Defrance, also in the lower chalk — but with respect 

 to these some doubt exists. 



The following genera, more or less immediately 

 allied to the genus Venus, constitute a subfamily or 

 section of the Cardiidse, in part the Venerida; or 

 Venerina; of some writers. Mr. Gray, who recog- 

 nises a family per se in the Veneridae, places as the 

 first in his order Phyllopoda, to which succeeds the 

 family Cyrenldic, and next the family Cardiidse ; 

 thus establishing three families out of the Cardiacos 

 of Cuvier, or the Conchacea of De Blainville. The j 

 latter divides his Conchacea into the following sec- 

 tions : — 



1. Regular Conchacea with the lateral teeth dis- 

 tant. Genera Cardium, with its subdivisions ; 

 Donax, and Tellina, with its subdivisions ; Cyclas, 

 with its subdivisions ; Cyprina, and Mactra, with its 

 subdivisions ; and Erycina. 



2. Regular Conchacea without lateral distinct 

 teeth. Genera Crassatella and V'enus. 



3. Irregular Conchacea. 



Genera V^enerupis, with its subdivisions ; Corallio- 

 phaga, Ciotlia, Corbula, with its subdivisions; 

 Sphaena, and Ungulina. 



As, however, it is not our plan to enter minutely 

 into the arrangements of various writers, we shall at 

 once proceed to the genera of which our pictorial 

 specimens are representatives. 



And first the genus Cyrena : — Cuvier places the 

 genus Cyrena (and also Cyprina) as closely related 

 to Cyclas. The Cyrena?, he observes, are natives 

 of rivers, as are also the Cyclades ; the shell is thick, 

 somewhat triangular, and oblique, and covered with 

 an epidermis : it is distinguished from Cyclas by 

 having three cardinal teeth, instead of two. The 

 raollusk, which differs little from that of Cyclas, has 

 the two lobes of the mantle united at their posterior 

 third, and prolonged by two retractile siphons se- 

 parated to the base. 



2969.— The Dusky Cyrena 



(^Cyrena fiiscata). This species is described by La- 

 marck as a native of the rivers of China and those 

 of the Levant. It is of a brownish green colour, with 

 numerous transverse subimbricate furrows. The um- 

 bones and the inside of the valves are violet coloured ; 

 the lateral teeth are much elongated transversely, 

 and denticulated. 



M. Deshayes, in his last edition of Lamarck, enu- 

 merates fifteen recent and twelve fossil species. 



With respect to the genus Cyprina, it is closely 

 allied to Venus. The hinge has three unequal 

 teeth, ap))roximated at the base, subdivaricate 

 above ; a lateral tooth distinct from the hinge, but 

 sometimes obsolete. 



M. Deshayes remarks that Cyprina may be dis- 

 tinguished from V>nus by the following points : — 

 The mollusk of Cyprina has the two lobes of the 

 mantle united posteriorly, and they terminate on 

 that side in two very short siphons, or rather in two 

 perforations resembling those iu Cardia. These si- 

 phons are too short to require a retractor muscle, 

 and for this reason the impression o( the mantle is 

 always simple in true Cyprinae. In the Veneres the 

 animal furnished with longer siphons is provided 

 with a retractor muscle which produces a more or 

 less deep inflection of the pallia] mark. Moreover, 

 on all the Cyprinse there ought to be a posterior 

 lateral tooth on the border below the termination of 

 the ligament. The species are found in sandy mud, 

 at the mouths of rivers. 



2970.— The Common Cyprina 



{Cyprina vuUjaris). This species, synonymous 

 with or a mere variety of the Cyprina Islandica, is 

 found at the mouths of rivers in the Northern Ocean. 

 It is cordate in shape, transversely striated, and co- 

 vered with an epidermis. It occurs also in a fossil 

 state. The number of recent species, according to 

 M. Deshayes, is two ; of fossil seven ; but three 

 species are recorded by Dr. Fitton below the chalk, 

 which have to be added. 



We now turn to the genus Cytherea, which is a 

 mere subgenus of Venus : the hinge presents four 

 cardinal teeth in one valve, of which iliree are di- 

 vergent and one isolated ; and three cardinal teeth 



in the other valve. In Venus there are only three 

 teeth in each valve. 



Lamarck states that in Cytherea there are con- 

 stantly four teeth in ihe hinge, and that the fourth 

 tooth is very oblique, and always set in that part of 

 the border which comprises the funule. In many spe- 

 cies this tooth is indeed constant, but iu more than 

 twelve living and fossil species, which M. Deshayes 

 carefully examined, he traced a gradual diminution 

 in this tooth, till at length it became merely rudi- 

 mentary ; and he adds, that having in this rudimen- 

 tary stage escaped the notice of M. Lamarck, the 

 latter ]ilaced many species belonging to his Cythe- 

 rea in the genus Venus. Where, then, asks M. 

 Deshayes, is the division line to be drawn, and what 

 reasonable ground exists for the separation of the 

 two genera ? The same question may be asked re- 

 specting half of the genera in every department of 

 zoology ; seldom are they founded on philosophical 

 principles, and seldom have they the same relative 

 value. 



Of the genus Cytherea, M. Deshayes in his Ta- 

 bles enumerates eighty-five living species and fifty- 

 nine fossil ; but in his last edition of Lumarck he 

 reduces the number of living species to seventy- 

 eight, and of fossil species to nine. To the latter 

 are to be added six species described by Mr. Lea 

 from the tertiary beds of Alabama, and six from 

 beds below the chalk, enumerated by Dr. Fitton. 



2971, 2972.— The Spined Cytherea 



(Cytherea Diorte). Venus Dione, Linneeus. This 

 beautiful shell from the seas of America is re- 

 markable for the row of spines on the posterior 

 borders of each valve ; in some individuals they are 

 long and distant, in others close set and short. The 

 valves are transversely furrowed with elevated la- 

 mellae. In colour these species differ considerably ; 

 some species are roseate, others vinous, others more 

 or less tinged with purple. 



2973. — The White Cytherea 



(.Cytherea meretrix). In this species the valves are 

 smooth and white, with the posterior margin tinged 

 with purple ; the umbones are spotted with brown ; 

 some varieties are more or less marked with chest- 

 nut. 



Of the genus with three cardinal teeth in each 

 valve, to which the term Venus is mostly restricted, 

 we may adduce the following example : — 



2974, 2375. — ^The Canckli.ated V^enus 



( Venus canceUata). We figure tvi-o varieties of this 

 shell, which is girt with elevated tiaiisverse belts. 

 The colour is white, spotted with bfty or brown ; 

 the lunule cordate. It is a native of the seas of 

 America. 



The species of Venus are very numerous, and, 

 though occurring in most seas, are chiefly natives 

 of the warmer latitudes, and are generally to be 

 found at a moderate distance from the shore. 



From the genus Venus has been separated a group 

 to which the term Pallastra has been applied ; the 

 genus thus named reposes, says M. Deshayes, on 

 characters of minor importance than Cytherea. The 

 shell is delicate, with three narrow and approximated 

 teeth on the hinge of each valve ; but there is no 

 clear line of division to separate Pallastra from 

 Venus. 



2976. — The Pattern-shot Venus 



(Venus [Pallastra'] textile). This beautiful shell, 

 reminding us of some zigzag patterns, the produce of 

 the loom, is a native of the Malabar coast : the 

 shell is ovate, smooth, and of a pale yellow with 

 purplish scribbled or zigzag lines. 



2977.— The Common Venus 



(Venus vulgaris). Pallastra vulgaris. It is very 

 probable that this species really belongs to the 

 genus Venerupis. 



A distinct genus vfhich we may just notice is 

 Lucina of Bruguiore ; in which the shell is suborbi- 

 cular, with small pointed oblique umbones and two 

 divergent cardinal teeth (one bifid), which are 

 variable, and disappear with age. There are two 

 lateral teeth. 



The number of recent species is about twenty ; 

 but of fossil species about sixty-five are enumerated ■ 

 some occurring in strata below the chalk, others in 

 tertiary formations. 



With respect to the following genera, we are by 

 no means clear that they all belong to the present 

 family. Most of the species are borers by habit, 

 piercing stones and masses of coral, in which they 

 reside. They constitute the family Lithophages 

 (Lithophagida;) of Lamarck. 



The first genus to be noticed is Venerupis Cor 

 Venerirupis), the shell of which is described by M. 

 Rang as solid, striated, or radiate<l, a little elon- 

 gated, and gaping posteriorly ; the anterior side is 

 shorter than the posterior, which latter is generally 



