124 THE NAUTILUS. 



along with Margaritana ravenelliana Lea and they seemed to differ 

 from U. gibbosus Bar. sufficiently to warrant making a variety of 

 them, in which opinion Mr. Simpson of the National Museum con- 

 curred. Its place is between U. subgibbosus Lea and U. gibbosus 

 Barnes and while it occasionally has the white nacre of the former 

 species it is always larger but less massive, wider and has a darker 

 epidermis. 



It is also related to U. stonensis Lea and closely resembles that 

 species except in epidermis and nacre. Only three specimens out 

 of fifty had a pure white nacre, and those would be taken for ston- 

 ensis but for the darker epidermis. 



Margaritana marginata Say, vnr. truncata nov. 



Shell abruptly truncated behind, and more produced in front, 

 causing it to be nearly equilateral. More inflated and usually 

 larger than the typical form. 



Remarks. This well marked variety was noted by Mr. Say and 

 specimens were by him labelled in this name, but no description was 

 ever published, so far as known. It occurs in eastern as well as 

 western waters and into Virginia and Tennessee. 



DESCRIPTIONS OF NEW PISIDIA. 



BY DR. V. STERKI. 



Pis. splendidulum Sterki. 



Additional localities are: Upper Red Hook, N. Y., and New 

 Philadelphia, Ohio. 



Pis. abyssorum Stimpsnn, n. sp. 



Mussel small, moderately inflated, somewhat elongate and oblique 

 (most specimens somewhat rhombic), superior and inferior margins 

 moderately curved ; scutellum slightly, scutum rather well marked ; 

 posterior end rounded or slightly truncated above obliquely in pos- 

 tero-anterior direction, merging into the inferior margin with one 

 continuous curve ; anterior end a rounded angle situated rather in- 

 feriorly ; beaks slightly posterior, rather low, comparatively broad ; 

 color whitish to pale horn; surface polished, with fine, irregular 

 stria? ; shell very thin, translucent; hinge very fine, plate very nar- 

 row; cardinal teeth short, lamellar, thin, longitudinal, scarcely 

 curved, the superior of the left valve little anterior, quite small or 

 abortive; lateral teeth very thin, not high, the outer ones of the 

 right valve scarcely perceptible or absent; ligament small. 



