37 Ithaca Group 37 



The forms described as R. eximia and R. stephani appear to 

 ht varieties of the same species. The larger specimens sometimes 

 hav^e a width of one inch, and the strong angular plications char- 

 a(::leristic of R. stephani. The ratio of length and breadth varies 

 considerably in different individuals; generally the length is 

 slightly greater than the width, but in some individuals the 

 length and breadth have the ratio of 8 to ii. The majority of 

 the specimens are not more than ^ to y^ inch in width and 

 have the finer plications of R. eximia. 



Rhynchonella contraBa Hall. 



Lower part of the Ithaca group. 



Ryh^ichonella piignus Martin. 



This species which has heretofore been known only in the 

 Ithaca fauna, I have found in the Portage below the upper 

 Spirifer Icsvis zone. 



Leiorhynchus niesacostalis Hall. 



This species is very abundant in the Ithaca group, occurring 

 in some layers almost to the exclusion of other species. The 

 specimens vary greatly in size, the largest measuring about i^ 

 inches at the greatest width, while average specimens measure 

 about y^ of an inch. Leiorhyjichus sinuatus is probably a small 

 v'ariety of this species. 



Cryptonella eudora Hall. 



This species appears to have a very limited vertical range. It 

 occurs abundantly near the middle of the Ithaca group. 



Atrypa reticularis Hall. 



This species becomes abundant in the upper part of the Ith- 

 aca group. It seems to be entirely absent from the Portage 

 and the lower part of the Ithaca fauna. 



Atrypa aspera Hall. 



Abundant at a few localities in the upper part of the Ithaca 

 group. 



Chonetes lepida Hall. 



This is a common Portage species. It occurs in the Ithaca 

 group, but less frequently. 



Chonetes scitula Hall. 



Specimens of the C. scitula type occur associated with C. seti- 



