440 CYPRINID^. 



orifices. The foot is thick and liuguiform, resembling- that 

 of the Venerida. 



Whilst the last family appears to have increased in num- 

 bers upwards in time, until its maximum was attained in 

 existing- seas, this seems to have been chiefly developed 

 during past epochs, and to be now in progress of diminu- 

 tion. The two groups may be regarded as to a certain 

 extent successive in time. 



'M. Alcide d'Orbigny styles this family Astartid^, and 

 gives as prominent characters the absence of a distinct 

 buccal siphon, and the shortness of the foot, both of which 

 do not apply to any of the animals of the group examined 

 by us. In the last arrangement by Mr. J. E. Gray, Circe is 

 placed in one division of the Venerida, Cyprina in another, 

 whilst Astarte and Isocardia form part of distinct families 

 in a separate order from that to which the Venerides them- 

 selves are assigned. It would be interesting to know upon 

 what principle so curious a disposition of these genera has 

 been proposed. 



CYPRINA, Lamarck. 



Shell more or less suborbicular, solid, equivalve, closed, 

 smooth, or concentrically striated, Invested with an epider- 

 mis ; beaks prominent, incurved ; no lunule ; margins 

 smooth. Hinge composed of a lateral tooth, and three or 

 four primaries in one valve, and of three primaries only in 

 the other. Ligament well developed, conspicuous ; pallial 

 impression simple, muscular impressions oval. 



Animal suborbicular ; its mantle freely open, with plain 

 or serrated edges. Siphonal orifices sessile, or nearly so, 

 their margins fringed, the branchial largest. Foot large, 

 lingulform ; labial palps moderately long, triangular. 



