SCAMMON : THE UNIONID.E OF KANSAS, PART I. 365 



Length. Height. Breadth. Um. ra. 



88 62 47 0.06 (317.1) 



85 60 44 .09 (460.1) 



85 62 47 .045 (Coll. K. S. A. C.) 



62 48 37 .06 (461.1) 



78 54 45 .08 (462.1) 



Q. 'plena is found in the Ohio, the Cumberland and the 

 Tennessee river drainages, and extends west into Kansas, 

 Indian Territory, and Arkansas. It is found only in the 

 clear-water rivers of the southern drainage in the state. It 

 is fairly common, being found on the gravel-bars of the 

 larger streams. Plena varies considerably in its elongation. 

 The older specimens are much longer in proportion to their 

 height than are the younger ones. The shells have either 

 pink or white nacre, in my experience. The form having the 

 pink nacre is the more abundant. 



The main differences between this form and Q. soUcla and 

 Q. ebenus is noted under the descriptions of those species. 

 Q. pyramidata is much more liable to be confused with j)lena 

 than are either of the above species ; it is, however, a higher 

 shell, with more elevated umbones and a more flattened or 

 emarginate anterior margin. 



Quadrula pyramidata Lea. Not figured. 



Unio pyramidatus Lea. Trans. Amer. Phil. Soc. , iv, 1834, p. 109, pi. 

 XVI, fig. 39. 



Unio mytiloides Deshayes Encyclopedie M<^thodique, Historic des Vers, 

 par Bruguiere et Lamarck, n, 1830, p. 586, pi. ccxLix, fig. 4. 



Shell moderate in size, heavy, thick anteriorly, much thinner 

 ventro-posteriorly, elliptical, triangular in outline. Anterior 

 margin straight or slightly incurved above, rather abruptly 

 rounded below ; ventral margin straight or a little incurved, 

 slightly oblique, short ; posterior margin slightly rounded ; 

 dorsal margin quite long, oblique. Umboidal ratio, from 

 0.05 to 0.09. Beaks very much elevated, incurved and de- 

 curved. Anterior umboidal slope very abrupt, and bearing a 

 very slight furrow running from the anterior side of the um- 

 bones to the upper part of the anterior margin ; lateral slope 

 much higher anteriorly than posteriorly, and bearing a nar- 

 row, radial flattened area, corresponding in position to the 

 radial furrow in some related forms ; posterior slope very 

 abrupt and slightly incurved. Epidermis dark brown, with 



