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, var. truncata nov. 
Shell abruptly truncated behind, and more produced in frent, 
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.,SPERKT. 
Pis. splendidulum Sterki. 
Additional localities are: Upper Red Hook, N. Y., and New 
Philadelphia, Ohio. 
Pis. abyssorum Stimpson, 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 
striz ; 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. 
