BRACHIOPODA. 



343 



valve, in the middle of a triangular deltidium, which 

 reaches to the lower valve; this opening is sometimes 

 closed in old shells. 



This is a doubtful genus. 



Strophomena. Rqfinesque. (Leptagonia M'Coy.) — 

 Shell nearly flat, or slightly and regularly curved, semi- 

 circular, or semi-oval, with a long, straight hinge ; a tri- 

 angular area on the natter valve, with a triangular arched 

 deltidium, at the apex of which there is sometimes a small 

 round opening; a narrow straight area on the convex 

 valve ; valves usually regularly radiated ; the interior of 

 each valve has three straight plates, or elevated lines, 

 diverging from the hinge, and bounding the muscular im- 

 pression, the fore part of the muscular impression not 

 being bounded by any ridge or elevation. — Fossil. 



Rafinesque's original description seems to have been 

 lost : the above is by Mr. Sharpe, in the Journal of the 

 Geological Society. 



Calceola. Lam. — Shell equilateral, 

 inequivalve, triangular ; umbones separated 

 by a large triangular disk in the lower 

 valve ; cardinal margin straight, linear, 

 dentated; lower valve large, deep; upper 

 valve flat, semiorbicular, forming a kind 

 of operculum to the lower.* 



A very singular shell, known only in the fossil state. 



Family 4. — CRANIADJE. 



The mouth arms are fleshy, without any shelly support. 

 The shell is calcareous ; the under valve is attached by its 



* Sow. Conch Manual. 



z 4 



