274 PALAEONTOLOGY OF NEW YORK. 



abruptly rounded below and sub-truncate above, produced considerably 

 beyond the beaks. 



Valves moderately convex; the point of greatest convexity is a little 

 anterior to the middle. 



Hinge-line oblique ; length less than one-half the length of the shell. 



Beaks small, appressed. Umbonal region moderately convex, gently 

 merging into the general surfiice of the shell. 



Test strong, marked by regular laminae of growth and fine concentric 

 striae. Interior unknown. 



The specimen described has a length of 65 mm., and a height of 42 mm. 



The shell is proportionally longer than in M. Schoharie and not so broad 

 posteriorly. It is not so extended anteriorly as in M. madlmta and M. mytiloides, 

 and not so prominent in the umbonal region. Compared with M. alta, the 

 liinge is shorter, less oblique, posterior margin much more regularly rounded, 

 basal margin more convex, .and the umbonal slope less distinctly defined. A 

 larger collection of specimens for comparison may show that this species has a 

 near relation to M. complanata. 



This species has been identified with M. perovata, but a comparison shows it 

 to differ in the broader arcuation of the basal margin and the greater exten- 

 sion of the anterior end. 



Formation and locality. In the upper member of the Upper Helderberg 

 gi-oup, Clarence Hollow, Erie county, N. Y. 



MODIOMORPIIA LTNGUIFORMIS. 



PLATE XXXIV, FIGS. (15?) 16, 17. 



Modunnorplia HnffuifarmU, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 34, fijfs. 15-17. 



1883. 



Shell of medium size or larger ; form sub-elliptical ; length less than twice 

 the height; basal margin gently curving; posterior margin abruptly rounded; 

 cardinal margin arcuate, greatest elevation near the middle of its length. 

 Anterior end abruptly rounded, extending but little beyond the beaks. 



