c. 



pusilla, 



c. 



setigera^ 



a 



scitula, 



c. 



lepida, 



c. 



coronal a f 



c. 



logani. 



148 i TWENTIETH REPORT ON THE STATE CABINET. 



parallel to the sides of the triangular fissure. They appear on the crest 



of the area as little pustules or elongated tubular spines, which may be 



either vertical to the hinge-line or directed outwards. 



In the Upper Helderberg and Hamilton groups, we have the following 



species : 



Ckonetes hemispherical 



C, arcuata, 



C. acutiradiata, 



C. lineata, 



C. yandellana^ 



C, mucronata^ 



C. deflecta, 



The occurrence of this last named species in the TuUy limestone is a 

 fact of great interest, carrying back the appearance of this species to a 

 much earlier epoch than had heretofore been known. The species occupies a 

 limited area in the Tully limestone of New- York, and is not known in the 

 Chemung group within the State ; though found in the sandstones of the 

 same age in Ohio, and in the beds at the base of the Burlington lime- 

 stone in Iowa and Illinois. 



In the Chemung group we have the recurrence of Chonetes scitula, C. 

 lepida and C. setigera; with a new and remarkable species, the C. muri' 

 cata, which has the apex truncated and the surface of the ventral valve 

 ornamented with spines, but having the vascular markings peculiar to the 

 genus. 



Under the head of Productus and Strophalosia, the relations of 

 these genera and of the Genus Aulosteges are discussed. The Devo- 

 nian species, sometimes referred to Strophalosia, are shown to have a 

 narrow area, but with internal vascular impressions like Productus. The 

 absence of an area in the Genus Productus is not uniform, as is shown in 

 P. costatus of the Carboniferous system in America; and the same has 

 been shown by Mr. Davidson to be true of P. sinuatus and P. semireticu- 

 latus of Europe. 



In comparing the American Devonian forms of Productidae with the 

 Strophalosia of the Permian system, the former have a greater width 

 on the hinge-line, and in this respect more resemble typical Productus; 

 while the narrow cardinal area and hinge-teeth assimilate them with Stro- 

 phalosia. Notwithstanding this feature, the vascular markings are like 

 Productus. 



At this epoch we have the earliest known appearance of these forms, the 

 type of which becomes extravagantly developed in the Carboniferous period, 



