GUELPH FAUNA IN THE STATE OF NEW YORK 



43 



specimens before us from Rochester and Shelby, as well as those described 

 from the Coralline limestone of eastern New York, agree in having the pli- 

 cations obsolete, while they distinctly show the fine concentric striae with 

 minutely setose edges, characteristic of that species. Hall expressly states 

 that these Coralline forms possess no distinctive features from the Niagaran 

 specimens of this very variable species, and he therefore had " no hesitation 

 in referring the specimens from the Niagara and the Coralline limestone to 

 the same species." At the same time it seems that there is, in the progress 

 of this species, a decided tendency toward the development of smooth forms, 

 as is evinced by the replacing of the strongly plicated shells of the Roch- 

 ester shales by the smooth forms in the Coralline and the Guelph dolomites. 



In the upper horizon on Oak Orchard creek a few faintly ribbed speci- 

 mens indicate the derivation of the smooth mutation from the typically 

 costate form. But they also contrast strongly with the highly plicate forms 

 found abundantly in a fossiliferous limestone layer in the Lockport lime- 

 stone above the lower Shelby bed and among which there are found no 

 smooth specimens. In the lower fauna Spirifer is entirely absent. 



A similar smooth expression of Spirifer crispus in the dolomites 

 of the Manlius horizon has been recently observed by A. W. Grabau in 

 western New York and described as Spirifer eriensis. 1 Dr Grabau 

 emphasizes the very close relation of his form with the Coralline (Coble- 

 skill) limestone variety of Spirifer crispus for which he has proposed 

 the varietal term corallinensis. These smooth varieties of the species 

 thus extend to the top of the Siluric. 



The larger form is too robust to be considered a variety of S p. cris- 

 pus. It is also distinguished by the subtriangular outline, and the long 

 extended beak of the pedicle valve. The sinus is extremely shallow and 

 can hardly be characterized as flanked by folds. Parts of the shell adhering 

 to the cast exhibit concentric imbricating lines. A comparison with S p. 

 bicostatus at once suggests itself, but the form from the Guelph dolo- 

 mite is still larger than the typical forms of that species, has the extremities 



■Geol. Soc. Am. Bui. n. 1900. p. 366. pi. 21, fig. 2a, b. 



