SCAMMON : THE UNIONID^ OF KANSAS, PART I. 345 



rough ; posterior scars large, faint, confluent. Pallial line im- 

 pressed andcrenulate for the anterior two-thirds of its length. 

 Dorsal muscle scars variable in shape and number. Cavity of 

 the beaks deep, of the shell moderate ; branchial depression 

 well outlined. Nacre white, iridescent posteriorly. 



Quadrula undulata var. latecostata Lea. Not figured. 



Unio latecostatus Lea, Proc. Amer. Phil. Soc, IV, 1845, p. 163. 



Distinguished from the species proper by the finer and 

 more regular undulations and thinner and more compressed 

 shell. 



Quadrula undulata var. pilsbryi Marsh. Not figured. 

 Unio pilsbryi Marsh, Nautilus, v, 1891, p. 1. 



Differs from the species in being produced ventro-pos- 

 teriorly and in bearing plications which tend to break up into 

 short transverse bars. 



Q. undulata has very extensive distribution. It is found 

 throughout the Mississippi basin north into Canada and the 

 St. Lawrence drainage, south in the Alabama river system, 

 west almost to Mexico. It is a common species in all the 

 drainage areas of Kansas, but is, perhaps, most abundant in 

 the smaller tributaries of the Kansas river. Here it stands 

 next to Lampsilis Juteola in abundance, and the riffles are 

 often covered with the shells. The reported range is as far 

 west as the Smoky Hill river at Salina ; it probably goes 

 much further west. On Chapman creek, a tributary of the 

 Smoky Hill, it is very abundant ; in a lot of about 150 shells, 

 fully fifty per cent, were (J. undulata, but there was not a 

 single specimen of the nearly related Q. plicata in the lot. 



The variety latecostata is found only in the southern drain- 

 age. The best examples I have seen were from Lake Thayer, 

 in Neosho county. Simpson (20) has stated that it is in 

 Kansas that this form merges with the true species. This I 

 believe to be true, for while transitional forms between the va- 



