CIIONETES OF THE CHEMUNG GROUP. 145 



wliile its surface markings, when entire, consist of fine closely arranged striae, 

 and in a partially exfoliated condition it is marked by two sets of excentric 

 lines crossing each other, which give a very peculiar aspect ; while the absence 

 of spines upon the surface readily distinguishes it. 



I have seen that species only from the beds below the Burlington limestone, at 

 Burlington ; and we do not know what modifications may take place in its cha- 

 racters in distant localities. 



The Chonetes muricata, in its truncate apex and spiniferous surface, has the 

 external aspect of Strophalosia ; but a careful examination shows all the dis- 

 tinctive features of Chonetes. A single specimen, partially preserving the shell 

 on the hinge-line, shows an area on the ventral valve of nearly a line in width in 

 the centre, the dorsal area being about one-third as wide. 



Geological formation and localities. In the arenaceous and semicalcareous beds 

 of the Chemung group, at Ellington in Chautauqua county, New-York ; and at 

 Meadville, Pennsylvania. 



In addition to the species which are clearly recognised in the Chemung group, 

 there are casts of the interior and impressions of the exterior of one or two 

 others which cannot be satisfactorily referred to any known forms, and which 

 are not in a condition to be described as distinct species. 



In the eastern part of Ohio there is a species of Chonetes occurring in beds 

 from sixty to one hundred feet below the Carboniferous conglomerate, and in a 

 position somewhat higher than the beds from which the principal part of the 

 fossils in New- York are obtained, which bears a close resemblance if not identity 

 with the C. illinoisevsis. It occurs in association with C. logani, and is distinguished 

 by its larger and more gibbous form and finely striated surface, having from 80 

 to 120 fine subequal striae upon the surface of the ventral valve. When exfoliated, 

 the surface is finely and regularly punctate between the striae. The cardinal 

 margin bears jjiiree or four slender diverging spines on each side of the beak (not 

 "five or six oblique spines on each side of the beak,"). as in C. illinoisensis. 



Paljsontology IV. 19 



