156 PALEONTOLOGY OF NEW YORK. 



The specimens of tliis \;ii-it'ty are uniformly smaller. They have been 

 observed mainly in the soft shales at Pratt's falls, OiKnidaga county, wiiilc the 

 large erect forms are common in the coarse shales and grits of the gn>u|i in tin- 

 eastern portion of the State, and in Madison county. 



In examining and comparing the extreme forms, the ililferenco is striking 

 and distinctive. (For exam2)lo, the erect forms on plate xi, and tiie oblique 

 forms, figures 5 to 11, plate xiii.) But in the study and comparison of a 

 series of several hundred specimens, the intermediate forms appear to unite 

 the whole under a single species. 



To facilitate the examination, the oblique forms, represented in figures 5-11 

 of plate xiii, are here designated as G. eredum, var. obliquum. 



The description of Avicula ereda, and A. crudformis, given by Mr. Conrad, 

 are as follows, loc. cit. : 



" Avicula ereda, pi. 12, fig. 5. — Direct ; independent of the wings, of ovate 

 " acute outline ; left valve ventricose, concentrically wrinkled, or marked with 

 " lines of growth ; apex prominent, narrow, acutely rounded ; posterior wing 

 " elongated, pointed ; basal margin uniting with the lateral margins in a regular 

 " curve or arch. 



Locality — Hamilton, Madison county. New York. 



" Avicula crudformis, Conrad, loc. cit. : " Elevated, with both ears greatly 

 "elongated. Locality — NearOneonta: This species is remarkable for the great 

 "proportional height; very little ()lilir[ue. Height oA inches." 



The name of A. crudformis has precedence in point of time, but the name 

 of A. ereda has been adopted because the description and figure entitle it to 

 recognition, and the former name is only applical)le to the more extravagant 

 forms of the species illustrated on plates xi and xii. 



