OF THE UNITED STATES. 63 



I name this species in memory of the many favors I 

 have received from my friend Joseph Barabino, Esq., of 

 New Orleans. 



2. I. alveatus, (S. G. M.) PI. xvii, fig. 4. 



Specific character. Ventricose, with prominent concen- 

 tric ribs, and a profound and broad longitudinal sulcus on the 

 posterior side; between this and the extremity is a similar in- 

 dentation. 



This species is found with the preceding, and is almost 

 as variable. The annexed drawing was made from a 

 small but admirably preserved specimen ; but I have one 

 in my possession three inches long. 



Avicula. 



1. A. laripes, (S. G. M.) PI. xvii, fig. 5. 



Specific character. Ovato-triangular, with about twenty nar- 

 row costae, which become gibbous towards the margin. 

 Length, one inch and a half. 



2. A very oblique, ventricose, obscurely striated cast, 

 less than inch in length. 



Both these fossils are from the marls of Delaware. 



PlNN 



A. 



Fragments of casts not unlike P. tetragona, Min. Conch. 

 pi. cccxiii, fi^. 1. I also obtained fragments of the shell 

 of another species from the calcareous strata of New Jer- 

 sey, and Mr. Conrad found others in Alabama. 



