158 DIMYARIA. 



** Shells with an internal ligament, and not gaping at the sides. 



Genus 51.— ERYCm A.— Lamarck. 



Generic Character — Transverse, subinequilateral, equi- 

 valve, rarely gaping ; with two primary teeth, unequal, di- 

 verging, with a pit interposed; lateral teeth two, oblong, 

 compressed, short, and inserted ; ligament internal, situated 

 in a pit. 



There is much difficulty in judging of the hinges of this genus, owing 

 to their equivocal character. 



Erycina striata. — The Striated Erycina. Plate 

 XVII. fig. 21. Yellowish-green, with strong transverse 

 striae. One inch long. Inhabits the Indian ocean. 



Genus 52 CRASSATELLA. 



Generic Character. — Inequilateral, suborbicular, or trans- 

 verse, close; primary teeth two, somewhat divergent, with 

 a hollow at the side ; lateral teeth, none or obsolete ; liga- 

 ment internal, inserted into a pit in the hinge. 



There is a close affinity betwLxt this genus and Mactra and Lutraria ; 

 like them it has the hgament internal, and attached to the primary 

 cavities of each valve, but when closed, the shells fit exactly, and do 

 not gape like these genera. The hgament in some of the species is 

 partially external, but less visible than in the genus Amphidesma. 



Crassatella Kingicola. — The King's Island Crassa- 

 TELLA. Plate XVIII. fig. I. Ovate, orbicular, yellowish- 

 white, with obsolete rays; very minutely striated trans- 

 versely ; the umbones somewhat plicated. Two inches long. 

 Inhabits the sea at King's Island, New Holland. 



Genus 53.— LIGULA Montagu. 



Generic Character. — Equivalve, with a broad transverse 

 tooth in each valve, projecting inwards, furnished with a 

 pit for the reception of the cartilage, and in some species a 

 minute tooth. 



