514 PALEONTOLOGY OF NEW YORK. 



MOD I ELL A, Hall. 1883. 



MODIELLA PYGM^A. 



PLATE LXXVI, FIGS 9-20. 



Ptfrinea pygiiuea, Conrad. Jour. Acad. Nat. Sci., Phila., vol. viii, p. 2.')1, pi. 13, fig. 15. 1842. 

 Cjfpricardinia pyffiiuta (Co.nkad), S. A. Millkr. Cat. Am. Pal. Fosa., p. 188. 1877. 



MitdieUa jrj/iriium (Conrad), Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 76, figs. 9-20. 



1883. 



Shell small, obliquely ol)Ovate; length one-third greater than the height. 

 Basal margin arcuate anterior to the middle, broadly and distinctly curving 

 to the post-inferior extremity. Posterior margin obliquely and broadly 

 curved. Cardinal line distinctly arcuate, reaching beyond the middle of the 

 length of the shell. Anterior end short, auriculate, limited by a depression 

 extending from just anterior to the beak to the basal margin and producing 

 a more or less distinct sinus. 



Valves very convex in the middle and upper portions of the shell. 



Beak^: sub-.anterior, small, closely appressed and incurved. Umbonal 

 slope not distinctly limited, rather prominent, arcuate, extending to the post- 

 inferior extremity. Along the middle of the cardinal slope there is some- 

 times a depression extending to the posterior margin. 



Surface marked by fine concentric striae, crossed by curving, radiating 

 striae which are more distinct on the body of the shell just posterior to the 

 sinus. In well-preserved specimens the junctions of the radii with the con- 

 centric striae are elevated into minute pustules. 



Mu.scular impressions and pallial line distinctly marked. Hinge-line with 

 a narrow groove posterior to the beaks. 



Three specimens measure respectively 10, 14 and 15 mm. in length, and 

 7, 9.0 and 10 mm. in height. 



The shell has the general form and external characters of a Modiola, with a 

 constriction on the antero-basal margin indicating the place of a byssal sinus. 



Formation and localities. In the shales of the Hamilton group at Pratt's falls, 

 Onondaga county, and on the shores of Skaneateles, Otisco and Cayuga 

 lakes, N. Y. 



