44 Bulletin 6 44 



Mytilarca chemungensis Hall. 



This species is common at station 4-5, and from a few local- 

 ities in the Ithaca group. 



A single specimen from the Spirifer IcBvis bed at Ithaca falls 

 differs from the ordinary specimens of M. chemungensis in its 

 erecft form and small size. 



Mytilarca umbonata Hall. 



From the Ithaca group. — Hall. 



Leptodesma sociale Hall. 



This is a characfleristic species of the Portage and Ithaca shale, 

 and occurs less frequently in the Ithaca group. Different indi- 

 viduals show great variation in the extension of the wing, the 

 gibbosity of the shell, and the obliquity of the body. Some 

 specimens correspond closely to Hall's figures of L. potens and 

 L. potens var. juvens, but they probably represent variations of 

 L. sociale. 



Leptodesma sp? 



Imperfecft specimens of one or two large species of Leptodesma 

 have been found in the upper part of the Ithaca group. 



Leptodesma naviforme Hall. 



From the Ithaca group. — Hall. 



Pterinea ( Vertum^nia) reproba Hall. 



Common in the upper part of the Ithaca group. 



PterinopeHien ereBus Hall. 



This is a rare species. A few specimens have been obtained 

 from the Ithaca group at the University quarry and in Fall 

 creek. 



PterinopeBen suborbicularis Hall. 



Occurs in the Ithaca group. — H. S. Williams. 



AviculopeSlen cancellatus Hall. 



From the Ithaca group. — H. S. Williams. 



Aviculope£len fasciculatus Hall. 



This species is rather rare in the Ithaca group. One speci- 

 men referred to this species is from station 2-14. 



AviculopeBen striatus? Hall. 



Specimens which appear to belong to this species are found 



