LAMELLIBRANCHIATA. 171 



below, Hat above, becoming convex towards the beak, which is low and 



scarcely reaches the hinge. 



Hinge-line straight, about equal to the length of the valve. 



Beaks anterior, acute, directed forward. 



Ear large, extended, defined by a broad sulcus and marked byssal sinus. 

 Wing large, expanded; margin concave; extremity abruptly acute. 



Test thin, marked by fine concentric striae of growth, which on some 

 parts of the surface are crowded into fascicles, producing ridges or undula- 

 tions. These are somewhat regular over the whole of the left valve, 

 and stronger on the anterior part; on the right valve they are without 

 regularity. The right valve also shows radiating lines which appeal' to 

 belong to the shell structure, and are quite conspicuous in partialh exfoliated 

 specimens. The striae are crowded and lamellose on the anterior margin 

 and adjacent to the byssal sinus; on the wing they are closely and evenly 

 arranged. 



Interior unknown. 



One of the imperfect specimens described has an approximate length of 

 61 mm., height 55mm., and hinge-line about 55 mm.; the measurement 

 along the axis of the body, from the beak to the post-basal margin, is 

 75 mm. 



The two specimens observed are crushed, and the characters of the left valve 

 are very much obscured, while the right valve preserves more nearly its true 

 proportions. It differs from the other species of this group in the concave 

 form of the right valve. In surface markings it is very similar to L. Sayi, 

 but the concave right valve is a very distinguishing feature. The shell is 

 large and thin, and has suffered compression and distortion in the process of 

 imbedding in the soft shales. 



Formation and locality. In the soft shales of the Hamilton group, Canandai- 

 gua lake, Ontario county, N. Y. 



