ORTMANN: monograph of the naiades of PENNSYLVANIA. 177 



Alasmidonta (Alasmidonta) undulata (Say) (1817).'^^ 

 Alasmidonta undulata (Say) Simpson, 1914, p. 494. 



Plate XI, fig. 7. 

 Records from Pennsylvania: 



Say, 1817 (Delaware River). 



Gabb, ISGl (Delaware, Schuj'lkill, and Wissahickon, Philadelphia; headwaters of Frankford Creek, 



Montgomery Co.) 

 Bruckhart, 1869 (Lancaster Co.) 

 Hartman & Michener, 1874 (Chester Co.) 

 Harn, 1891 (western Pennsylvania) .''° 

 Schick, 1895 (Canal at Manayunk, Philadelphia Co.; Munckinipattus Creek, Glenolden, Delaware Co.; 



Neshaminy Creek, Bucks Co.) 

 Ortmann, 19096, p. 207. 



Characters of the shell: Shell rather small, and rather thick, chiefly in its 

 anterior part. Outhne sub triangular, subovate, or almost subeUiptical; generally 

 comparatively short and high, more or less narrowed and pointed behind. Lower 

 margin more or less convex. Upper margin straight, forming or not forming an 

 angle with the obliquely descending posterior margin. Beaks more or less inflated, 

 and somewhat elevated above the hinge-line, situated more or less anteriorly. 

 Beak-sculpture extremely heavy, but somewhat variable. There are specimens with 

 much heavier sculpture than others. Sculpture consisting of four or five bars, 

 which are angular and much elevated posteriorly, straight or very little sinuated 

 in the middle, rounded and low anteriorly, running up to the beaks upon the 

 posterior slope as fine, but distinct, converging lines, and, in addition, there are 

 several similar radiating lines behind them, as well as in front of the beaks. (See 

 Marshall, 1890, fig. 11.) Upon the posterior slope there are sometimes irregular, 

 oblique corrugations, but in most cases, they are absent. 



Shell more or less swollen, lateral faces gently convex, with an oblique pos- 

 terior ridge, which is rounded and often indistinct. Posterior slope somewhat 

 compressed, rarely subtruncate. 



Epidermis greenish, yellowish, reddish-brown, brown, or black, with more or 

 less distinct dark green to blackish rays, which are broader or narrower, straight, 

 uninterrupted. Old shells are often uniformly black-browm. Often the posterior 

 slope is lighter than the rest of the shell, with more distinct, sharper, and finer 

 rays. Frequently there are lighter or darker concentric bands. Growth-rests 

 rather indistinct. 



'25 Not 1816. 



126 This species certainly is absent from the Ohio-drainage. Harn's specimens may have come from 

 the headwaters of the West Branch of the Susquehanna (See Ortmann, 19096, p. 180). 



