CONCHIFERA. 



275 



odon Stutchbury ; Thalassina Quenstedt") — Shell (accord- 

 ing to Koninck) mostly thin, equivalve, inequilateral, 

 closed, transverse, furrowed; the hinge consisting of a 

 single cardinal tooth with an oblique pit near it, and two 

 distant lateral teeth ; the front side tooth of the right, 

 and the hinder side tooth of the left valve lock in ; two 

 simple muscular impressions, and a single small pallial im- 

 pression ; a double ligament, the one inward lying in the 

 above-named pit, the other outward, short ; the curved 

 bosses rest on each other. — Fossil. 



Megalodon. Sow. — Shell equi- 

 valve, longitudinal, acuminated at the 

 umbones, thick ; hinge forming an 

 incrassated septum across the cavity 

 of the shell, with a large bifid tooth 

 in the right valve, and one irregular, 

 and one pointed in the left ; ligament 

 long, ex tern al. * — Fossil . 



Very like the genus Cardita. 



Megalodon cucullatics. 



Family 14. — CARDITA CEA. 



The animal has the mantle lobes entirely separated, 

 with the exception of a small portion which divides the 

 opening from the breathing and other ducts ; the foot com- 

 pressed, with a byssus ; the mouth has one lip tentacle on 

 each side. The shell is free, regular, equivalve, inequi- 

 lateral; the hinge has in each valve two unequal teeth, 

 the lateral teeth present, or absent. Living in the sea in 

 temperate and warm latitudes. 



* Sowerby's Conch. Manual. 



t 2 



