LAMELLIBRANCHIATA. 379 



length, abruptly recurving at the post-basal extremity and obliquely truncate 

 above. Cardinal line nearly straight, scarcely declining posteriorly. Ante- 

 rior end short, obliquely truncate above, at the lunule, and abruptly rounded 

 below, having an angle at the junction of the two lines. 



Valves regularly convex in the lower and posterior portions, becoming 

 gibbous above and especially on the post-umbonal slope. 



Beaks sub-anterior, prominent, large, strongly incurved. Umbonal slope 

 obtu.sely sub-angular, and extending to the posterior extremity, with a faint 

 indication of a plication on the post-cardinal slope. Valves marked by a 

 distinct cincture extending from the beak, more or less obliquely, to the 

 basal margin anterior to the middle of its length. 



Surface marked by fine concentric striae, which are obscurely visible in 

 the cast ; and by strong concentric undulations which mark the anterior and 

 central portion of the valves, becoming obsolete on the umbonal ridge. Inte- 

 rior unknown. 



Five specimens measure respectively 29, 30, 32, 35 and 44 mm. in length, 

 and 17, 17, 21, 17 and 24 mm. in height. 



This shell has been identified as Grammysia (Allorisma) Hannibalensis, of 

 Shu.m.'VRD, but compared with authentic examples of that species from the 

 original locality it is found to differ in its more elongate form, sub-angular 

 umbonal slope, more oblique cincture, and more strongly defined concentric 

 folds. 



Formation and localities. In the Chemung group, at New Albion, Olean, Port- 

 ville, and Little Genesee, N. Y. ; and at Warren, Pa. 



Grammysia undata. 

 plate lxi, rig. 23; plate lxiv, fig. 30; and plate xcm, fig. 21. 



Kdwmlia undata. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. G4, fig. 30. 1883. 



Shell below the medium size; ovate sub-elliptical; length about one-third 

 greater than the height ; basal margin gently curving, nearly straight, and 

 slightly constricted anterior to the middle of its length. Posterior margin 



