52 
PALEONTOLOGY OF NEW YORK. 
of the valve, extending farther toward the posterior than toward the 
anterior margin. 
Beak obtuse, rounded, central to the body of the shell, depressed, not 
rising above the hinge-line, nor extending to the hinge-margin; umbonal 
region moderately convex, not defined laterally. 
Anterior ear small, narrow-triangular, not well-defined; extremity very 
obtuse, rounded; margin slightly concave without a decided byssal sinus. 
Posterior ear triangular, more than twice the length of the anterior, and defined 
from the umbonal slope by the absence of the strong radii; extremity acute- 
angular ; margin marked by a broad, rounded sinus. 
Test marked by about 40 strong, elevated rays, which are somewhat 
flattened along their summits; usually alternating with one or two sharp or 
rounded rays, crossed by very fine, sharp, concentric striae. The radii 
gradually diminish in strength towards the ears, where they are represented 
by elevated, narrow lines. 
Ligamental area marked by several longitudinal striae. Other interior 
characters not known. 
The height of the specimen is 97 mm., length 104 mm., hinge-line 44 mm. 
Three of the stronger rays occupy a space of 12 mm. at the basal margin. 
The specimen described is the impression of the exterior of a left valve; it is 
quite characteristic and very distinct from other known species in its form and 
surface markings. 
In ornamentation and general outline there is some resemblance between this 
shell and L. macrodontus, but it is less convex, the rays are more elevated, and 
more sharply defined. The geological horizons of the two species are also 
widely separated. 
Formation and locality. In coarse, arenaceous slates of the Upper Chemung 
group, at Montrose, Susquehanna county, Penn. 
