SCAMMON : THE UNIONIDvE OP KANSAS, PART I. 325 



county in the southern drainage area, and I have received 

 specimens from as far west as Hays, from Big creek, a tribu- 

 tary of the Smoky Hill river, in the Kansas drainage. The 

 largest specimens that I have seen from the state were from 

 Rock creek, Douglas county. This species is a lover of quiet 

 water and muddy or somewhat sandy banks. It is in fact 

 unfitted to survive other conditions on account of its fragile 

 shell. 



There is no species with which this form can be easily con- 

 fused ; the extreme fragileness of the shell and lack of umbones 

 will distinguish it from the young of A. grandis. It varies 

 but little. 



Anodonta suborbiculata Say. Plate LXXIII. 



Anodonta suborbiculata Say, New Harm. Diss, (newspaper form) , Jan. 

 29, 1831. 



Shell very large, thin, slightly compressed, suborbiculate 

 in outline. . Anterior margin flatly curved ; ventral margin 

 almost circular ; posterior margin rounded for the first fifth 

 ventrally, and very slightly incurved for the remaining four- 

 fifths ; dorsal margin straight or very slightly curved. Um- 

 boidal ratio variable, from 0.25 to 0.40. Umbones very low 

 and flat, and ornamented with four or five pairs of slight 

 nodules arranged in a series which represent degenerate 

 double-looped ridges. Anterior and lateral umboidal slopes 

 flatly curved ; posterior umboidal ridge low but distinct ; pos- 

 terior slope slightly excavated. Epidermis straw-yellow to 

 dark brown in color, smooth and shining except for the pos- 

 terior umboidal slope, which is slightly roughened ; fine green 

 rays are sometimes present. Lines of growth fine and con- 

 tinuous. Ligament dark and rather stout. 



Interior : Hinge line very thin. Muscle scars large, very 

 faint. Pallial line very faint. Cavity of shell rather large, 

 of beaks very slight. Nacre white, varying to a light salmon, 

 deepest in color near the umbones, very iridescent. 



Dorsal pos- 

 Um. ra. terior angle. 



^■40"^ 125° j ^^°^^- ^^"- ^^^^' ^^^-^ 

 '.32 110° (Coll. W. C.) 



This species extends from Nebraska and Illinois south to 



4-Ball., Vol. Ill, No. 9. 



