CHONETES OF THE CHEMUNG GROUP. 141 



netes logani, which I have shown to occur in the Tully limestone of New- 

 York ; and although distinct species, are not in themselves evidence of 

 a higher geological position. 



From the fact that the three species first indicated have this great 

 vertical ran^e, we might infer that they would also show a wide geogra- 

 phical range; but this does not seem to hold true regarding them, in the 

 line of exploration which has been followed. 



The Chonetes coronata which is known in Eastern, Central and Western 

 New- York in the Hamilton group, is also known in the same horizon in 

 Illinois and Iowa ; but it has not been recognized in the Chemung group 

 of New- York, Pennsylvania or Ohio, nor elsewhere in that horizon. 



If we regard the Chonetes pusilla as a variety of C laticosta or C. deflecta, 

 that species has a wide geographical range, since it occurs on the Missis- 

 sippi river in Illinois ; but it has not been found in New- York or else- 

 where above the horizon of the Hamilton group. On the other hand, the 

 C. logani, which begins its existence in the Tully limestone or the upper 

 limit of the Hamilton group, ranges on the west to the base of the Car- 

 boniferous limestone, though unknown in the Chemung group of New- 

 York. 



I may, in the subsequent pages, call attention to other similar examples, in 

 reference to geological and geographical distribution of species. 



Chonetes scitula. 



PLATE XXII. , 



[ Reference page 130 of this volume.] 



This species, in the shaly beds, preserves impressions of the exterior 

 and casts of the interior, showing the characteristic surface markings, the 

 spines of the area margin, etc. 



In the coarser sandstones it is somewhat larger and coarser in its mark- 

 ings; and sometimes the striae are nearly equal, presenting a character 

 of surface observed in the Hamilton group. 



The casts of the ventral valve show the filling of the minute tubes 

 which correspond to those seen in the shell of the specimens from the 

 Hamilton group. 



