110 



PROCEEKISQS OF THE ACADEMY OF 



[1884. 



PTEROPODA. 



Tibiella Marshi (nov. gen. et nov. spec.)* 



Shell thin, tubular. The closed end little convex. The lower 

 part, about one third of the whole length, of 

 a circular section, then by tapering a little 

 forming a kind of a neck, above which the 

 shell is of a rounded trigonal section. Aper- 

 ture dilated. 

 Length, 3^ mm. 



Locality. — Eocene sand from Claiborne, 

 Ala. 



Remarks. — If the figured specimen is adult, 

 in the young ones the apex ma}^ be perhaps 

 acute and afterwards partitioned off, as in the genus Tripter-a 

 Quo}^ et Gaimard ( Guviera Rang). 



This genus is allied to Tibiella, and the latter is perhaps a sub- 

 genus of the former. 



Pteropoda are described from the Miocene and Oligocene, but 

 as far as I am acquainted with the litei'ature this is the first 

 Pteropod from the Eocene. 



OPISTHOBRANCHIAT^. 



Balla biumlilicata (nov. sp.). 



Shell small, moderately thick, oval, the upper end obliquely 

 truncated and umbilicated, the lower end somewhat tapering. 

 Last whorl most prominent at about one- 

 third of the whole length. Outer lip? Inner 

 lip below with a large trigonal thin callus, 

 which covers a minute umbilicus. Surface 

 with revolving lines, disappearing at both 

 ends and generally' most distant from each 

 other at about the middle of the shell. A 

 strong magnifying glass shows that these 

 lines are furrows, looking like pearl-ribbons, 

 which structure causes the surface to look 

 at some places as if it were minutely longitudinally costated. 

 Length, 2i mm. 



* Genus name from the resemblance to the tibia of mammals. This 

 species is dedicated to Professor Marsh, who enabled me to work by sup- 

 plying me from his library with a large part of the necessary literature, 

 which I could uot get elsewhere. 



