* Ligament seen externally or double. 



Genus 47.--AMPHIDESMA.— ZamarcA. 



Generic Character Inequilateral, transverse, suboval, or 



somewhat rounded ; vnth. sides slightly gaping ; hinge with 

 one or two cardinal teeth, and a narrow groove for the inter- 

 nal ligament ; ligament double, the external short, the inter- 

 nal fixed in the internal grooves. 



These possess a peculiar character which distinguishes them from 

 all other bivalves, namely, the two ligaments. 



Amphidesma reticulata. — The Reticulated Amphi- 

 DESMA. Plate XVII. fig. 24. Suborbicular, sub-diaphanous, 

 compressed, finely reticulated ; yellowish- white. One inch 

 and a quarter long. Inhabits the West Indian seas. 



Genus 48.— SOLEMY A.— Zawarc^. 



Generic Character. — Inequilateral, equi valve, transversely 

 elongated, obtuse at the extremities, with the epidermis 

 smooth, shining, and projecting beyond the margin; beaks 

 not prominent and hardly distinct ; a dilated, compressed, 

 somewhat oblique cardinal tooth in each valve, slightly con- 



156 DIMYARIA. 



Although having some affinity to the genera Crassatella, and Ungu- 

 lina, they are at once distinguished by the inequahty of their valves, 

 and the strong primary elevated tooth. I 



Corhula Nucleus The Kernel Corbula. Plate XVII. i 



fig. 20. Somewhat triangular, strong, with the under valve i 

 much larger than the upper one ; transversely striated ; \ 

 covered with a thick, brown epidermis. Half an inch long. : 

 Inhabits the British seas. 



TRIBE IV. MACTRACEA. 



Equivalve shells, frequently gaping at the lateral ex- 

 tremities ; with an internal or partly external ligament, and 

 the animal having a small compressed foot. 



