160 CO^GRYLIA—DITHYRA. 37. 



37. GYTREU^A— LAMARCK. 



Testa suborbicularis seu transversa, csquivalvis, inoequilateralis, clausa. 

 Cardo valv<s dextrce dentibus quatuor, tiibus basi approximatis, unico 

 remotiusculo sub areola; valvoe sinistros dentibus trlbus, rariiis qua- 

 tuor, basi approximatis. cum fovea anticd remotiusculd : lateralibus 

 nullis. Ligamentum externum. 

 Shell somewhat orbicular or transverse, equivalve, inecjuilateral, with 

 four teeth in the right valve, three of them close together at the 

 base, and one remote under the areola ; in the left valve three 

 teeth, rarely four, close together at the base, with a remote hollow 

 on the anterior side : lateral teeth none. Ligament external. 

 From the Venus tribe this family is separated by sufficiently di.s- 

 tinctive characters : the four teeth in one or both tbe valves ; and 

 when there are but three in one valve, a remote oval hollow parrallel 

 with the margin. All the British species, as far as they are yet 

 known, have the internal margin very entire. 



Chiono. Cytherea testd ovuto-cordatd nitidd transversim substriatd, areola 

 lanceolatd. 

 Shell oval heart-shaped glossy and slightly striate transversely, with 

 the areola lanceolate. 



Tab nost. 8. fig. 11. 

 Venus Chione. Linn. Syst. Nat. p. 1131. 

 Gmelin, Syst. p. 3272. 

 Turton, Linn. Syst. iv, p. 222. 

 Pennant, Brit. Zool. iv. p. 206. tab 54, fig. 2. 



