568 PALEONTOLOGY OF ILLINOIS. 



anterior margin of the dorsal valve. None of the specimens show the 

 cardinal process entire, but as far as its characters can be made out, it 

 seems to have been much as in Chonetes. 



The most remarkable character of this shell, however, remains to be 

 noticed. That is, its extremely coarse punctate structure, and the 

 unusually close arrangement of the punctures, which are so large as to 

 be nearly visible to the unassisted eye. As seen by the aid of a com- 

 mon single pocket lens, they present on the inner surface of the dorsal 

 valve much the appearance and arrangement of the cells of a delicate 

 Chcetetes, the spaces between them being much less than the diameter 

 of the pores themselves. They appear to diminish rapidly in size, how- 

 ever, as they approach the external surface, near which they seem to be 

 a little less than the diameter of the spaces by which they are separated. 

 As we have never seen such a shell structure as this in any species 

 known to possess the characters of the genus CJionetes, nor indeed to 

 any other known Brachiopod, we are very strongly inclined to believe 

 our shell really belongs to an uudescribed genus. The fact that there 

 appears to be no sockets in the cardinal margins of its dorsal valve for 

 the reception of teeth in the other valve, would also favor the conclusion 

 that it is not a true Chonetes. Nevertheless, we prefer to place it, pro- 

 visionally, in that genus, until specimens can be obtained showing the 

 dorsal valve, with the muscular impressions and other generic charac- 

 ters. Should it be found, as we believe it will, to be a new generic type, 

 we^vould suggest for it the name Isogramma (too?-, equal; YP^-W^I a line), 

 in allusion to the remarkable equality of the concentric lines of the sur- 

 face. 



To whatever genus our shell may really belong, it is evidently very 

 closely allied, even specifically, to a form figured by Mr. DAVIDSON, 

 from the Carboniferous Limestone of Scotland, in his valuable Mono- 

 graph of the British Carboniferous Brachiopoda, Vol. II, Part V, pi. 55, 

 fig. 13. Mr. DAVIDSON referred his shell, with much doubt, on the 

 authority of Dr. DE KONINCK. to Chonetes concentrica, of the latter 

 author. We fully concur with Mr. DAVIDSON, however, in the opinion 

 that it is distinct from Prof. DE KONINCK'S species,* as it is much longer, 

 and instead of being marked with only twelve to thirteen large concen- 

 tric ridges, has about thirty-seven regular, more concentric lines. In 

 our species there are about twice the number of lines seen on that 

 figured by Mr. DAVIDSON, in specimens of the same size ; and as this 

 character is remarkably uniform in all our specimens, we cannot believe 

 it otherwise than a specific difference. 



Locality and position Upper Coal Measures; Marion county, Illinois, 



* It is due to Professor DE KOXINTK that we should state that it was only doubtfully he referred the 

 English specimen to his species. 



