THE NAIADES OF MISSOURI 317 
ductive as far as able to determine from sterile material that is 
only at hand. Glochidia not known. 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES:—Shell elongate - elliptical moder- 
ately inflated, obtusely rounded before, pointed behind, dorsal 
line acurate, ventral with a slight long upward curve; disk smooth; 
post-umbonal ridge rounded; beaks‘low, faintly sculptured con- 
centrically across two radiating ridges; epidermis olive green or 
yellowish rayed with capillary lines, some arranged in bundles. 
INTERNAL STRUCTURES:—Cardinals double in both valves, 
post-cardinal of right valve rudimentary; interdentum long, 
rather narrow, notched; scars well impressed; beak cavity shallow 
branchial, however, large with deep impression in female shell; 
nacre white to pearl blue. 
Sex Length Height Diameter Locality 
9 95 x 50 x 28 ——(Spring R., Webb City) 
Geom x, 4d, Ka 25 ——(White R., Hollister) 
o 85 x 45 x 24 ——(Jack’s Rork, Shannon Co.) 
9 60 x 30 x 17.5——(White R., Hollister) 
This last specimen being young and well preserved shows 
the fine characteristic rays more distinctly and while the beak 
sculpture would show more distinctly than in older shells yet it 
is even obscure here and does not add anything to the above 
description of the external shell structures. 
MISCELLANELUS REMARKS:—Before Simpson had_ studied 
the soft parts of this species he had considered it as F. dilatata 
(=U. gibbosus); however, its peculiar marsupial characters would 
not only discriminate, but also its different beak sculpture and 
dissimilar hinge. The beak sculpture of dilatata is one of the most 
emphatic among the Nazades while that of this species is one of 
the most obscure; besides the interdentum of the former is broader 
and thicker while the branchial impression of clintonensts dis- 
tinguishes it from all other species outside of its genus. This 
species lies very close to its fellow, facsiolaris, and it is considered 
by some as merely a variety of it, but perhaps it is a good species 
on account the lack of the splotched rays and larger, heavier, 
thicker shell of the type for /ilipisartia.' Clintonensis is abundant 
* Recent studies by Dr. Ortmann and Mr. Frierson have resulted in 
the positive conclusion that the Unio occidentalis Conrad (Monog., VII, 
