266 PALEONTOLOGY OF NEW YORK. 



It is referred to the genus Gosselettia of Barrois, from the Devonian of 

 Sp;iiii. on account of its similarity of external form and the strong cardinal 

 teeth ; otherwise it has all the characters of Mytilarca. 



Formation and localities. In the shales of the Hamilton group, Fultonham, 

 Schoharie county, and Onondaga county, N. Y. 



Gosselettia retusa. 



PLATE XXXIH, FIGS. 1, > 

 Gfossdettia retusa, Ball. Pal. N. Y.. vol. v, pt. 1. Plates and Explanations: PI. 3d, tig-s. 1. 2. .Ian.. 1883. 



Shell of medium size : body very oblique, rhomboid-ovate, sub-arcuate ; length 

 one-third greater than the height ; ventral margin nearly straight for two- 

 thirds of the length, inflated at the byssal opening and concave below, 

 thence abruptly curving into the broad basal and dorsal margin. 



Valves equal, regularly convex in the posterior part and gibbous in the 

 umbonal region ; the point of greatest convexity is above the middle. 

 The ventral umbonal slope is sub-angular. Ventral side flat. 



Hinge-line short. Beaks acute, prominent, directed a little forward and 

 incurved. 



Test of moderate thickness, marked by lamellose concentric lines of 

 growth which at irregular distances are crowded into fascicles. 



Ligamental area and interior unknown. 



The specimen described has a length of 49 mm., height 32 mm., breadth 

 30 mm. 



This species differs from G. triquetra in its proportionally longer form, which 

 is less expanded posteriorly ; hinge-line shorter and less oblique to the body of 

 the shell ; and the ventral umbonal slope is less angular along the length. 



Formation and locality. In the Hamilton group, Eighteen mile creek, Erie 

 county, N. Y. 



