0RISKANY FAUNA OF BECKAFT MOUNTAIN 49 



Cyrtina varia gp. nov. 



Plato 6, fig. 15-82 



1892. Cyrtina rostrata and G. cf. dalmani Clarke, op. cit. p. 414 

 The specimens of Cyrtina in this fauna are quite variable in 

 size and proportions. There is a small, tetrahedral form with high, 

 slightly concave and relatively short cardinal area, which suggests Cyr. 

 dalmani Hall of the Helderbergian fauna, but is of larger size 

 with narrower plications (5 or 6 on each lateral slope) and broader 

 intervals. This form passes into one with very elongate cardinal 

 area, like some of the forms from the Oriskany sandstone which have 

 been regarded as young of Cyr. rostrata Hall. 1 There is again 

 a large shell which sometimes attains the full size of Cyr. rostrata, 

 with slightly arched, cardinal area and rather short hinge-line. These 

 shells bear from 5 to 8 plications on the lateral slopes, have 

 the median fold depressed or slightly furrowed on top, with a simi- 

 larly flattened median sinus. The surface in all is finely pustulose 

 and crossed by sharp, concentric lines. As there is at present no 

 satisfactory basis for separating these various shells, and as they can 

 not all be referred to any of the described species, they are here 

 considered as individual expressions of the same species. 



Chonetes hudsonica sp. nov. 



Plate 7, flg. 1-6 



1892. Chonetes sp. n., Clarke, op. cit. p. 413 



This is the only normally convex Chonetes found in this fauna. 

 The shell is of medium or small size, transverse in outline ; hinge-line 

 marking the greatest width of the shell; lateral margins subparallel 

 for a short distance and rounding rather abruptly to a nearly trans- 

 verse anterior margin. Surface of the pedicle-valve quite uniformly 

 convex, with a faint median sinus seen only over the anterior 

 portion of the valve. The surface striae are fine, round and close 

 together, with very narrow interspaces. They increase rapidly and 

 irregularly by bifurcation and implantation. Very fine, concentric 



1 See Paleontology of New York. v. 3, pi. 96, fig. 1, a and b. 



