OF THE UNITED STATES. 39 



5. A. Conradi. (S. G. M.) pi. 16, fig. 1, 2, 3, and 

 pi. 19, fig. 4. 



Specific character. Much compressed; one complete volu- 

 tion and part of a second, the smaller being received into and 

 concealed by the larger : five or six rows of tubercles on each 

 side, the outer ones terminating at the peripheral margin, the 

 inner ones at the internal margin of the whorl ; tubercles 

 united by sub-angular, slightly curved costae. Periphery sub- 

 convex, and marked with three or four delicate, longitudinal 

 lines. Septas innumerable, extremely tortuous and intricate. 

 Largest diameter nearly two inches. Thickness half an inch. 

 PI. xvi. fig. iii. 



I dedicate this species, the most beautiful fossil 

 hitherto found in this formation, to its discoverer, my 

 estimable friend T. A. Conrad, Esq. Mr. C. found it 

 abundantly at Prairie Bluff, Alabama, in the older cre- 

 taceous deposits. So variable, however, are its forms 

 that I was at first disposed to consider myself in posses- 

 sion of three distinct species, which however, upon a 

 comparison of upwards of fifty individuals, appear to 

 have their essential characters, in common. The most 

 remarkable of these varieties are the following. 



Variety Jl. PI. xvi. fig. ii. 



More ventricose, outer tubercles larger, inner ones almost 

 obsolete : costas more distant, and larger. I had proposed for 

 this fossil the name of A. gulosus, which will serve should it 

 not prove identical with the former. 



Variety B. PI. xvi. fig. i. 



Ventricose ; costae and tubercles remarkably distinct. This 

 shell at first sight resembles an Argonauta, but it is a true Am- 



