DIMYAIRA. 139 



groove divided in the middle of the margin ; ligament internal, 

 inserted in a pit. 



A remarkable feature in this genus is the cavity being divided into two, 

 the one at the end of the other : the ligament is partially visible. 



UnguUna transversa. — The Transverse Ungulina. Plate 

 XVII. fig. 22. Transversely round, rugose, of a yellowish- 

 brown colour. 



** Shells with an internal ligament, and the shells not gaping 

 at the sides. 



Genus 51.— ERYCINA.-Zawiarc*. 



Generic Character. — Transverse, subinequilateral, equivalve, 

 rarely gaping ; with two primary teeth, unequal, diverging, 

 with a pit interposing ; 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 transverse, 

 close ; primary teeth somewhat divergent, with a hollow at the 

 side ; no lateral teeth, nor obsolete ones ; ligament internal, 

 inserted into a pit in the hinge. 



There is a close affinity betwixt this genus and the Mactra and Lutraria ; 

 like them it has the ligament internal, and attached to the primary cavities 

 of each valve, but when closed, they lit exactly, and do not gape like these 

 genera. The ligament in some of the species is partially exterior, but less 

 visible than in the genus Amphidesma. 



Crassatella Kingicola. — The King's Island Crassatella. 

 Plate XVIII. fig. 1. Ovate, orbicular ; yellowish white ; with 

 obsolete rays ; very minutely striated transversely ; the umbones 

 somewhat plicated. Tv/o inches long. Inhabits the sea at 

 King's Island, New Holland. 



Genus 5^.— LilGVLh.— Montagu. 

 Generic Character. — Equivalve, with abroad transverse tooth 



