SCAMMON : THE UNIONIDiE OF KANSAS, PART I. 333 



cavated in the right valve to form a socket for the anterior 

 left pseudocardinal. Anterior muscle scars not deeply exca- 

 vated but large. Posterior scars large, fused, lightly out- 

 lined. Pallial line slightly impressed anteriorly, outlined 

 posteriorly. Dorsal muscle scars pitted, numerous on pos- 

 terior face of pseudocardinals. Cavity of the beaks slight, of 

 the shell moderate, greatest in females. Nacre white, iri- 

 descent posteriorly. 



S. complanata is found in the Mississippi drainage north of 

 the Arkansas river and in the St. Lawrence drainage. It is 

 a common species in all the drainage basins of Kansas, and 

 has been reported as far west as Wichita and the Solomon river 

 at Minneapolis. It ranks close to Larajisilis luteola in abun- 

 dance in the streams of the northeastern part of the state. 

 Although most abundant in water from six to twelve feet in 

 depth and in a mud bottom, smaller specimens may often be 

 found in company with such forms as Quadrula plicata and 

 Tritogonia tuberculata in swift-flowing water of a foot or less 

 in depth and embedded in a gravelly bed. It attains a size 

 equal to any Unio in the state. It possesses a strong muscu- 

 lature, is a rapid burrower, and is very tenacious of life. 



Genus UNIO Retzius, 1788. 



"Shell inequilateral, oval to elongated, rounded in front 

 and pointed or biangulate behind, with a more or less devel- 

 oped posterior ridge, often becoming slightly arcuate when 

 old; beaks only moderately full, generally sculptured with 

 coarse ridges, which run parallel with the growth lines, or are 

 somewhat doubly looped, sometimes broken and showing fine 

 radiating lines behind ; surface smooth, slightly concentrically 

 ridged or pustulose ; epidermis rather dull colored, rayless 

 or feebly rayed ; hinge plate narrow, two pseudocardinals and 

 two laterals in the left valve, and one pseudocardinal and one 



♦From Minneapolis, Kan., high-school collection. 



