228 C O N C H O L O G Y 



However, I declare my appellation far 

 tliefe Shells is from their rhombic or lo- 

 zange fhape : for if one of this genus be 

 laid down, or held, and its contour traced, 

 the refult will be the figure of a Rhomb or 

 Lozange. This figure proceeds from the 

 clavicle or turban, which is generally fi- 

 tuated about the middle of the Shell, 

 running out into very (harp or acute an- 

 gles with the top and bottom, and there- 

 by the whole Shell fairly exhibits a rhom- 

 bic fhape, or contour. 



There is fome reafon to furmife, that 

 many of thefe Shells are only growths of 

 the next genus, or winged Shells. How- 

 ever, as it is not the cafe of all of them, 

 and that they all now wear this defcribed 

 appearance, I imagine it is neceflary to 

 form this genus. 



This genus" is not numerous, but eon- 

 tains pretty Shells ; and fome kinds are 



very large and heavv. 



There 



