348 KANSAS UNIVERSITY SCIENCE BULLETIN. 



proximately 0.20. Umbones prominent but not high, marked 

 with coarse lines and small nodules. Anterior umboidal slope 

 fully rounded ; lateral slope well rounded, and together with 

 the anterior is marked with obscure, low, small, triangular- 

 shaped elevations ; in some cases the dorsal margin of the 

 anterior slope is marked with a few small undulations. Pos- 

 terior ridge well marked, rounded, with a series of from 

 three to five large irregular nodules which vary greatly in 

 their prominence. Posterior slope flat and more or less un- 

 dulated. Lines of growth rounded and continuous. Epider- 

 mis horn color or russet, marked with numerous triangular 

 patches of dark green, which extend only a short distance up 

 from the ventral margin. Ligament fairly strong, long, dark 

 chestnut. 



Interior : Pseudocardinals rather small, low and pyramidal, 

 double and sometimes trifid in each valve. Anterior cica- 

 trices small, quite deep, sometimes fused; posterior scars of 

 moderate size, very faintly outlined, confluent. Dorsal 

 cicatrices small and located on the lower surface of the inter- 

 dentum. Pallial line impressed in the anterior half. Nacre 

 pure white, iridescent posteriorly. 



Posterior 

 Length. Height. Breadth.* Um. ra. ventral 



angle. 



97.5 40.5 30 0.20+ 137° (185.1) 



100 39.5 30 .21 134° (186.1) 



96.5 41 30.5 .21+ 130° (186.2) 



87 37 26.5 .20 131° (186.3) 



Q. cylindrica ranges from the Ohio, the Cumberland and 

 the Tennessee river systems west to Kansas. It is found in 

 Kansas only in the clear-water streams of the southern drain- 

 age — the Spring, the Neosho, and the A^erdigris. Although 

 seeming to be nowhere abundant, it is not a rare species in 

 the streams mentioned. Its favorite habitat is bars of gravel 

 or shingle in a rather swift current. The thick and nodu- 

 lous shell fits it admirably for these conditions. 



This is one of the most distinct and easiest recognized 



Unios found in Kansas waters. At first sight the elongate 



shell makes it appear out of place among the other members 



of its genus, but all the members of the small group to which 



♦This measurement is taken through the umbones. 



