L56 PALEONTOLOGY OF NEW YORK. 



The specimens of this variety arc uniformly smaller. They have been 

 observed mainly in the soft shales at Pratt's falls, Onondaga county, while the 

 large erect forms arc 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. erectum, var. obliquum. 



The description of Avicula erecta, and A. cruciformis, given by Mr. Conrad, 

 are as follows, loc. fit. : 



"Avicula erecta, pi. 1^, tig. 5. — Direct: independent of the wings, of ovate 

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

 " lines of growth ; apex prominent, naiTOW, 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 cruciformis, Conrad, loc. cit. : "Elevated, with both ears greatly 

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

 "proportional height; very little oblique. Height o\ inches." 



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

 of A. erecta has been adopted because the description ami 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. 



