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 umhonal 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 stria?. The radii 

 gradually diminish in strength towards the ears, where they are represented 

 by elevated, narrow lines. 



Ligamental area marked by several longitudinal stria?. Other interior 

 characters not known. 



The height of the specimen is 11" mm., length 104 mm., binge-line 44 mm. 

 Three of the stronger lays 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. 



