MaPiYland Geological Survey 143 



Occurrence. — Eomney Formation, Hamilton Member. Ernstville. 

 Collections. — Maryland Geological Survey; American Museum of Nat- 

 ural History. 



Genus LEPTAENISCA Beecher 



Leptaexisca australis Ivindle 



Plate XI, Figs. 1-5 



Leptaenisca australis Kindle, 1912, Bull. U. S. Geol. Survey, No. 508, p. 78, 

 pi. iv, figs. 8-12. 



Description. — Outline variable, as shown in figure; length generally 

 less than width; hinge line somewhat shorter than greatest width of shell. 

 Shell concavo-convex. Ventral valve moderately convex. Surface marked 

 by fine radiating striae, which are clearly defined only in the anterior part 

 of the shell, and which are crossed by very fine concentric striae and 

 stronger lines of growth. The muscular pit of the ventral valve is bord- 

 ered laterally by the dental lamellae which curve toward each other slightly 

 near the anterior margin of the pit. These lamellae, as they extend into 

 the shell and away from the surface of the valve, are inclined laterally or 

 away from each other. A short, low, median septum extends across the 

 muscular pit from the posterior nearly or quite to the anterior margin of 

 the pit. Molds of the interior of the ventral valve indicate a strongly 

 postulose surface, increasing regularly in coarseness from the margin of 

 the shell to the margin of the muscular impression. The collection con- 

 tains a single, somewhat imperfect, mold of the interior of a dorsal valve 

 believed to belong to this species. The distinctly bipartite character of 

 the posterior portion of the cardinal process is shown and, somewhat 

 indistinctly, the quadripartite appearance of the anterior portion of the 

 process is seen. A low thick median ridge is present in the anterior part 

 of the mold. 



All of the species of this genus previously described from America are 

 Helderberg shells. In surface characters they are quite unlike the present 

 species. Two of them appear from the figures to be nonstriated species, 

 but the third, L. concava, has radiating striae of unequal strength, each 



