LAMELLIBRANCHIA TA. 
171 
below, flat 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 strias 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 appear to 
belong to the shell structure, and are quite conspicuous in partially 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 55 mm., 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. 
