NAIADES OF MISSOURI 87 



of the beaks anteriorly; post-ridge inflated but not so sharply angled 

 as in juveniles of Fusconaia, 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., 1900, p. 82). It is 

 to be differentiated from the Eastern Tennessee Pleurobema argen- 

 teuni (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 Lanipsilis 

 very close to hiangulatus (Lea), is an interesting and remarkable 

 fact illustrating the power of environmental factors in the family."' 



Genus Elliptic Rafinesque. 



1 8 19 — Elliptio Rafinesque, Jour, de Phys. Chim. et His. Nat. 



1900b — Elliptio 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. Ulterbackii 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 shell 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 i 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." 



