Lamellibranchiata. 405 



Mytilarca lata. 



Mytilops {Modiola) lata, Hall. Pal. N. Y., vol. v, pt. 1. Plates and, Explana- 

 tions: PI. 33, fig. 22. Jan., 1883. 



Shell large ; body broadly sub-elliptical, abruptly narrowing toward 

 the beak on the dorsal side ; length one-third greater than the 

 height; byssal area slightly inflated, thence nearly straight for 

 almost three-fourths the length of the shell ; posterior margin 

 broadly rounded ; dorsal margin gently curved for two-thirds of the 

 length and then truncated in nearly a direct line to the beak. 

 Eight valve moderately convex in the posterior part, becoming 

 broadly convex in the middle, and somewhat gibbous in the urn- 

 bonal region. Left valve unknown. Hinge-line oblique; extent 

 unknown. Beak elevated, erect, acute. 



Test marked by rather coarse, elevated lines of growth . 



The specimen described has a length of 60 mm. and height 40 

 mm. 



This species somewhat resembles M. regular is, but the beak is more 

 anterior, the body wider and more convex, and the truncation of the 

 cardinal margin is much longer. 



Formation and locality. In the Chemung group, Randolph, Cat- 

 taraugus county, N. Y. 



GOSSELETTIA, Barrois. 



GOSSELETTIA RETUSA. 



Gosselettia retusa, Hall. Pal. N. T., vol. v, pt. 1. Plates and Explanations: 

 PI. 30, figs. 1, 2. Jan., 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, di- 

 rected a little forward and incurved. 



Test of moderate thickness, marked by lamellose concentric lines 

 of growth which at irregular distances are crowded into fascicles. 



