198 THE AMERICAN MIDLAND NATURALIST 
of the beaks anteriorly; post-ridge inflated but not so sharply angled 
as in juveniles of Fusconaza, nor so greatly rayed; beak sculpture 
also different in being more corrugated. 
_ ‘MISCELLANEOUS REMARKS:—The type shell is from the White 
River, Hollister, Missouri, collected by Mr. Utterback of St. 
Joseph, Missouri, for whom the species is named. Other specimens 
are at hand from contiguous territory. This species might possibly 
be the Pleu. argentea--‘‘ pannosa’’ of C. T. Simpson (indicated, 
but hardly described, in Proc. Nat. Sci. Phil., r900, p. 82). It is 
to be differentiated from the Eastern Tennessee Pleurobema argen- 
teum (Lea) with difficulty, having its beaks further in front, and 
higher than in argenteum. Specimens have been received under the 
heterogeneous names of L. ozarkensis (Call), ellipsiformis (Conrad), 
etc. But a series of about a dozen sent by Mr. Utterback from 
two or more localities proves the novelty of the form. The appear- 
ances of Truncilla and Pleurobema in the mountain streams of 
Arkansas and Missouri, together with an undescribed Lampsilis 
very close to biangulatus (Lea), is an interesting and remarkable 
fact illustrating the power of environmental factors in the family.’’? 
Genus Elliptio Rafinesque. 
1819—Elliptio Rafinesque, Jour. de Phys. Chim. et His. Nat. 
1900b—Eliptio Simpson, Proc. U. S. Nat. Mus., XXII, p. 700. (as 
section.) 
1912b—Elliptio (Raf.) Ortmann, An. Car. Mus., VIII, pp. 265-272. 
(Type, Unio [Elliptio] nigra Rafinesque). 
ANIMAL CHARACTERS:—Branchial and anal openings large 
with many small papillae; mantle connections between anal and 
supra-anal short, or moderately so; gills wide, very much round 
Being more doubted by some students that P. Utterbackit may not 
be distinct from L. ozarkensis (Call), Mr. Frierson would make this addi- 
tional description :— 
“Our shell is much more tumid at the beaks, or umbones; it is not furrowed 
on the post slope by the siphonal ridges as in ozarkensis; it is thicker; 
the anterior muscle scars are distinct, while in ozarkensis they are remarkably 
confluent. Our shel! is not dimorphic, while, if Call has not confused two 
species in one, his species is considerably so. Our shell differs especially 
from his figures 1 and 3, less so from fig. 4. Our shell has its whole facies 
of a heavier sort than ozarkensis. Our cotypes of the latter, from Mr. Call, 
are more inclined towards a Lampsiline structure, as indeed it is placed 
by C. T. Simpson. 
” 
