FAMILY 8. CONCHACEA (FLUVIATILIA). 87 



CYRENA, Lamarck. 



Testa sequivalvis, eequilateralis, subventricosa, plerumque solida, epider- 

 mide fusco-olivacea induta, umbonibus saepe erosa. Dentes utrius- 

 que valvse, cardinales tres, laterales duo, posticus ad cardinem pro- 

 pius admotus, anticus remotus. Ligamentum externum. 



We have already shown that the species appropriated by Lamarck to 

 the formation of this genus were included by Bruguiere with the Cyclades ; 

 we cannot but think, however, that they fully merit the distinction which 

 is here assigned to them, though De Blainville now fails to acknowledge it. 

 Their shells are always larger and thicker than those of the former genus, 

 are often much eroded, and differ in the number and position of the teeth. 



The Cyrense may be described as having an equivalve, equilateral 

 shell, which is rather ventricose, generally solid, and covered with an 

 olive-brown or blackish epidermis. There are three cardinal and two 

 lateral teeth in each valve, and of the latter one is situated near the 

 hinge, the other remote. The ligament is external. 



Example. 



PI. LXIII. 



Cyrena Sumatrensis, Sowerby, Genera of Shells, No. 5. Deshayes, 



new edition of Lamarck, vol. vi. p. 277. 

 Cyclas Sumatrensis, De Blainville. 



GALATHJEA, Bruguiere. 



Testa trigonularis, aequivalvis, insequilateralis, crassa, epidermide oliva- 

 ceo-virente induta, umbonibus plerumque erosa. Dentes cardinales 



