ridges are very uniform, and somewhat inversely imbri- 
cated. The anterior half is smooth. 
The handsome mass of silicized shells, upon which 
this rare species rests, was sent me for public use by 
Mr. Miller ; it is named affinis in the catalogue of his 
collection, from its resemblance, although distant, to 
Trigonia sinuata of Parkinson. 
