SCAMMON : THE UNIONID.E OF KANSAS, PART I. 355 



slightly oblique. Umboidal ratio not a constant, varying 

 from 0.15 to 0.35. Umbones vary in height, with moderate 

 inflation, to low and uninflated ; ornamented with from three 

 to five broken ridges, but free from pustules. Anterior um- 

 boidal slope fully rounded ; lateral slope fully or flatly rounded 

 and sometimes bearing a shallow and faint radial furrow ; 

 posterior slope generally incurved and often abrupt. The 

 posterior and lateral slopes bearing pustules which may be 

 numerous and cover most of the disk, or may be few and ob- 

 scure ; they are irregular in position and the pustules on the 

 opposite valves do not always correspond ; pustules lachry- 

 mosal in character but variable in size and outline. Epi- 

 dermis light horn to dark chestnut-brown in color, the younger 

 and lighter colored specimens ornamented over the umbones 

 and sometimes half-way down the disk with a very broad, 

 triangular green ray, which tends to break up into a number 

 of finer ones ; a similar ray is often present on the posterior 

 slope. Lines of growth well marked, darker than surround- 

 ing epidermis. Ligament of variable length, stout. 



Interior : Pseudocardinals rather heavy, ragged, double in 

 the left and single (with sometimes an anterior and pos- 

 terior auxiliary) in the right valve ; the left pseudocardinals 

 generally but not always joined dorsally ; right pseudocardi- 

 nal large and heavy, surrounded by a pit. Anterior ad- 

 ductor scars deep, semicircular or quadrant-like in outline, 

 extending somewhat under the anterior pseudocardinal in 

 the left valve. Posterior scars rather large for the size of 

 the shell, well impressed, distinct or fused. Pallial line im- 

 pressed about two-thirds of its length. Dorsal scars in a 

 row on the lower surface of the interdentum and upon the 

 base of the pseudocardinals. Cavity of the umbones quite 

 large, of the shell small. 



Interdentum broad and short. Laterals very variable in 

 length, curved or straight, highest posteriorly, set at right 

 angles to the longer axis of the pseudocardinals. Nacre satin 

 or pearly white. 



