156 
PALAEONTOLOGY OF NEW YORK. 
The specimens of this variety are uniformly smaller. They have been 
observed mainly in the soft shales at Pratt’s falls, Onondaga county, while the 
large erect forms are common in the coarse shales and grits of the group in the 
eastern portion of the State, and in Madison county. 
In examining and comparing the extreme forms, the difference is striking 
and distinctive. (For example, the erect forms on plate xi, and the 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. crutiformis, 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 crutiformis, Conrad, loc. cit.: “ Elevated, with both ears greatly 
“ elongated. Locality —Near Oneonta: This species is remarkable for the great 
“ proportional height; very little oblique. Height 3 h, inches.” 
The name of A. crutiformis 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 applicable to the more extravagant 
forms of the species illustrated on plates xi and xii. 
