TO GEOLOGY. til 



GENUS AST ARTE. Soiverby. (Crassina of Lamarck.} 



A. recurva. Plate 2. Fig-. 34. 



Description. Shell subrotund, angular before, emargin- 

 ate behind, deeply emarginate before the beaks, rather 

 compressed, concentrically and largely striate, deeply fold 

 ed behind ; substance of the shell rather thick ; beaks 

 very much elevated and recurved ; lunule large, deeply 

 impressed, cordate ; escutcheon long lanceolate ; pos 

 terior slope bicarinate ; teeth obliquely curved ; cicatrices 

 impressed ; margin finely crenulate. 



Diam. .2, Length .4, Breadth .4, of an inch. 



Observations. I have seen no species of this genus with 

 so elevated and recurved a beak as this. It is remarkable 

 for its curved teeth, the very deep impression of the lunule, 

 which, together with the recurviture of the beak, causes 

 the point of the latter to be quite hooked. The deep fold 

 or furrow, behind, forms on its edges sharp ridges, which 

 are imbricate. In one specimen, I observed longitudinal 

 striae diverging from the beaks and nearly reaching the 

 margin. 



Jl. Nicklinii. Plate 2. Fig. 35. 



Description. Shell transversely elliptical, subangular be 

 hind, emarginate at posterior basal margin, concentrically 

 and largely ribbed; beaks compressed, pointed; lunule 



