1193 



VENEIUD^E. 



VENERID/E. 



nal 



in it the following genera: Venus, Cytherea, Meroe, Triyona, Artemis, 

 Lucinopsia, Tapes, Vinerupix, Petricola, and Glaucomya. 



Our limits will only permit the illustration of this family by the 

 notice of a few genera, 



Cyrena. M. Deshayes, in hia last edition of the ' Auimaux sans 

 Vertebres,' remarks of the genus Cyrena that there exists a passage 

 between the two genera, but a point is arrived at where the species 

 become very distinct from Cyclas by reason of their thickness and 

 having one tooth more in the hinge. The animal of the Cyreiue which 

 M. Deshayes had seen did not differ essentially from that of Cyclas, 

 and approached nearly to that of Venus. It has the two lobes of the 

 mantle united in their posterior third, and prolonged on that side by 

 two siphons, which are separated to the base. They are furnished 

 with a small retractor muscle, which leaves a particular impression in 

 the shell. 



The number of species of Cyrena is about 25. They are mostly 

 found in tropical seas. There are about 75 fossil species found from 

 the Wealden upwards. 



C. ftucata, is brownish-green, with numerous transverse subimbricate 

 furrows ; violet within and at the uinbones ; the lateral teeth very 

 much elongated transversely and dentilated. It is a native of the 

 Chinese rivers and those of the Levant. 



Cyrina fiacata. 



M'jadetma. Shell equivalve, subtrigonal, covered with a greenish 

 epidermis. Hinge-teeth furrowed; two in the right valves connivent 

 at their base ; three in the other valve, the intermediate one advanced 

 and separated. Lateral teeth distant Ligament external, short, 

 projecting, convex. Nymphte prominent. (Lam.) Animal with a 

 thick subtrigonal body; the mantle large, simple, open below and in 

 front, closed posteriorly, and prolonged on that side into two equal 

 tubes separated at the base ; two unequal branchiae, the upper one 

 folded double ; four triangular buccal appendages ; mouth large ; foot 

 large, oblong, compressed, gubangular anteriorly. (Deshayes.) 



M. radiatum (Galalkea radiala, Lam. ; Potamop7i.Ua radiata, Sow.). 

 Under the epidermis milk-white, marked with violet towards its base, 

 and ornamented with violet rays, generally from two to four in number. 

 It u found in the rivers of Ceylon and of India. 



Cyprina. Shell equivalve, inequilateral, obliquely cordate; umbones 

 obiquely curved ; hinge with three unequal teeth, approximated at the 

 base, subdivaricate above ; lateral tooth distant from the hinge, on the 

 anterior side, sometimes obsolete ; nymphal callosities large, arched, 

 terminated near the umbones with an ovate lunule. Ligament external, 

 often partly immersed under the umbones. 



The species are generally found in sandy mud. 



C. filandica has the shell cordate, transversely striated, covered with 

 an epidermis; the anterior side subangulate. It is a native of the 

 Northern Ocean, at the mouths of rivers. 



Cytherea, Shell equivalve, inequilateral, suborbicular, trigonal, or 

 transverse. Four cardinal tei'th in the right valve, of which three are 

 divergent, approximated at their base, and one is entirely isolated, 

 situated under the lunule. Three divergent cardinal teeth in tho 

 other valve, and a fosset at a little distance parallel to the border. No 

 lateral teeth. (Lam.) 



Lamarck states that in Cytherea there are constantly four teeth 

 in the hinge. The fourth tooth is very oblique, and always set in 

 that part of the border which comprises the lunule. This tooth 

 is in fact constant in a considerable number of species ; but in 

 more than twelve, living as well as fossil, which M. Deehayes had 

 carefully examined, he saw this tooth diminish by little and little, 

 and become so rudimentary that, it having sometimes escaped 

 Lamarck's notice, the latter comprised many of this species in his 

 genus Venus, and placed the others among the Cytherece. If, says 

 M. Deshayes in continuation, these observations are just and it 

 will be very easy to verify them in a large collection of living 

 and fossil species of the two genera one may ask where the line 

 is to be drawn, and what reasonable ground exists for their 

 separation ? 



The number of species noted in the Tables of M. Deshayes is 85 

 recent and 59 fossil (tertiary). Of these C. erycina, C. chionc, C. nitl- 

 dula, C. citrina, C. exoleta, C. concentnca, C. lincta, C. rvfcscens, 

 C. multilamella, and C. renctiana are stated as occurring both recent 

 and fossil (tertiary). 



In the last edition of Lamarck the number of recent species 

 recorded is 78 ; and the number of fossil species is 9. Mr. Lea, in 

 his ' Contributions to Geology,' adds 6 species from the Claiborne Beds 

 (tertiary of Alabama). 



One of the most remarkable species is C. dione (Venus dione, Linn.). 

 This remarkable shell, of which there are many varieties, is obliquely 

 cordate in shape, of a rosy, rosy-purpurescent, purpurescent, or 

 vinous colour, transversely furrowed with elevated lamellce ; the pos- 

 terior borders of the shell are beset with spines, very long and distant 

 in some varieties, and short and close-set in others. 



It is a native of the seas of America. 



Oyprina Iilandica. 

 occur* below the Chalk. Ninety fossil species have been 



described. 



1'enia (Cythcrca) dune. 



