CYPRINIDA. 187 
diverging ; in Spherium, tubercular or of columnar shape, placed 
obliquely toward each other. 
EUPERA, Bourg., and FLUMINEA, RIVULINA and FOSSARINA, 
Clessin, are names of sections of the genus; they have but little 
distinctive value. 
CYRENOIDES, Joannis, 1835. 
Syn.—Cyrenella, Desh., 1833. 
Distr.—4 sp. River Senegal. The marine species are Diplo- 
dontz. Fossil,l sp. Europe. C. Dupontii, Joannis (cxiv, 49). 
Shell orbicular, ventricose, thin, eroded at the beaks; epidermis 
dark olive; ligament external, prominent, elongated ; cardinal 
teeth 3:2, the central tooth of the right valve bifid; muscular 
impressions long, narrow; pallial line simple. 
‘Animal with mantle open in front and below, margin simple, 
siphons short, united ; palpi moderate, narrow; gills very un- 
equal, narrow, united behind ; foot cylindrical, elongated. 
? CyctoconcHa, Miller, 1874. 
Distr.—C. mediocardinalis, Miller. L. Silur.; U. 8. 
Shell nearly circular, equivalve, concentrically sculptured, with 
a hinge-tooth and posterior and anterior laterals. 
Its pertinence to this family is doubtful. 
( Cardiacea.) 
Famity CYPRINID. 
Shell regular, equivalve, oval or elongated; valves close, solid; 
epidermis thick and dark; ligament external, conspicuous ; 
cardinal teeth three in each valve, and a posterior lateral tooth ; 
pedal sears close to, or confluent with. the adductors; pallial line 
slightly sinuous; siphons very short, with ciliated orifices ; foot 
thick, linguiform. 
Cyprina, Lamarck, 1812. 
EKtym.—Kuprinos (from Kupris), related to Venus. 
Syn.—Arctica, Schum., 1817. 
Distr.— C, Islandica (cxiv, 50-52) ranges from Greenland and 
the United States to the Icy Sea, Norway and England ; in 5-80 
fathoms water. It occurs fossil in Sicily and Piedmont, but not 
alive in the Mediterranean, Fossil, 90 sp. (D’Orbigny.) Mus- 
chelkalk—; Europe, U. S. 
Shell oval, large and strong, with usually an oblique line or 
angle on the posterior side of each valve; epidermis thick and 
dark; ligament prominent, umbones oblique; no lunule ; cardinal 
teeth 2°2, laterals 0—1, 1—0; muscular impressions oval, pol- 
ished ; pallial sinus obsolete. 
Animal with the mantle open in front and below, margins 
