SCAMMON : THE UNIONID^ OF KANSAS, PART I. 339 



oblique. Umboidal ratio in specimens examined averaged 

 0.12 to 0.18. Umbones ornamented with several coarse con- 

 centric ridges and a few fine radiating lines. Anterior slope 

 full and rounded ; lateral slope rounded anteriorly, occupied 

 by a broad, distinct radial furrow, which extends from the tip 

 of the umbone to the ventral margin ; on each side of the 

 dorsal half of the radial furrow is found a scattered row of 

 large, low tubercles which are often quite obscure ; posterior 

 umboidal ridge prominent. Posterior slope narrow, abrupt, 

 decidedly incurved dorsally, with broken transverse ridges on 

 the upper half. Epidermis dark horn, brown, black. Lines 

 of growth pronounced and continuous, imbricated marginally. 

 Ligament long, of moderate thickness, dark brown. Lunule 

 well developed. 



Interior: Pseudocardinals large, erect, ragged, double in 

 the left and single in the right valve, the right pseudocardinal 

 arising from a pit. Interdentum narrow, not very long. 

 Laterals long, straight, slightly oblique. Anterior adductor 

 cicatrices deeply excavated, rough, roundly triangular in out- 

 line ; anterior retractor scar deeply pitted ; posterior scars 

 large, lightly impressed, fused ; dorsal scars large on the 

 lower surface of the interdentum and the base of the pseudo- 

 cardinals. Pallial line impressed anteriorly, outlined pos- 

 teriorly. Cavity of beaks and shell moderate. Nacre pearly 

 white. 



C.) 



This species is found in the Cumberland, Ohio and Ten- 

 nessee river systems, and ranges west to Kansas. I have 

 seen only three specimens from Kansas. These came from 

 the Verdigris river at Coffeyville. They are of the typical 

 form. 



Pleurobema cicatricosum Say. Not tipjured. 



Unio varicosus Lea, Trans. Amer, Phil. Soc, iv, 1829, p. 90, pi. XL, 



fig. 20. 

 Unio cicatricosus Say, New Harm. Diss., ii, No. 19, 1829, p. 292. 



Shell large, thick, extremely ponderous in the region of 

 the umbones and anteriorly, elongately and roundly triangu- 



