410 PALEONTOLOGY OF NEW YORK. 



obliterates the radii. At the junction of these thickened portions, along the 

 base of the valves, the shell is excavated, leaving a tubular opening extend- 

 ing backward from the post-inferior extremity, as shown in figs. 27, 29 and 

 52 of plate Ixvii, and more fully in fig. 1 2 of plate xciv. 



Valves crenulated along their margins. Anterior muscular impressions 

 elongate, deeply impressed, narrower behind. 



Four specimens measure respectively 60, 47, 43 and 21 mm. in length, 

 and 30, 33, 26 and 13 mm. in height. 



This species resembles C. normale, in the Hamilton group, but that form is 

 usually more elongate with uniform simple ribs, and the interradial spaces are 

 marked by fine radiating striae. 



The specimens here referred to a single species are subject to great variation 

 in form and general aspect. The main differences are indicated in the follow- 

 ing varietal designations : 



Var. aifenuatum, Conrad. PI. 67, figs. 1-11. The specimens referred to this 

 form are apparently the young of C. cuneus, preserving numerous uniform, 

 fine radii upon the surface and the posterior extremity not abruptly 

 truncated. Specimens having these characters, as they become larger, 

 show a duplication of the radii and gradually assume the character of 

 C. cuneus. 



Var. trigonale, Hall. PI. 67, fig. 28; pi. 68, figs. 1, 4-16; pi. 94, fig. 11. 

 This name is given to the specimens occurring in the Corniferous limestone 

 and originally described as a distinct species. 



Var. nasutum, Hall. PI. 67, figs. 12-20. This name is applied to short, 

 triangular forms, which are broad and abruptly truncated behind, abruptly 

 contracted in front, with the anterior end nasute. The body of the shell 

 is marked by fewer radii than in characteristic forms of C. cuneus. 



Formations and localities. In the Schoharie grit, at Schoharie, and tlie Hel- 

 derberg mountains, and on the outcrop of the same formation in the neighbor- 

 hood of Rondout, Ulster county, and in Orange county, N. Y. ; in the Cornif- 

 erous limestone, at Williamsville, N. Y. ; at Dublin and Columbus, Ohio ; and 

 at the falls of the Ohio river. It also occurs at Cayuga and other places in 

 Canada West. 



The species, in its varieties of form, occurs "at Pendleton, Indiana, in a sand- 

 stone which probably represents the horizon of the Schoharie grit, 



