ORTMANN: monograph of the naiades of PENNSYLVANIA. 121 



in North Fork Hughes River, a tributary of the Little Kanawha, and, for the present 

 I regard this as a stray specimen. Rafinesque gives it from Kentucky, also Baker 

 (1898a, p. 60), but it is unknown from the Cumberland and Tennessee. The 

 distribution seems to be also very restricted in a southwesterly and westerly direc- 

 tion. The records from Arkansas and Iowa are ver^' vague, and certainly need 

 verification (for Iowa, see Geiser, 1910). It is absent from Call's Arkansas list (1895), 

 and from Scammon's Kansas list (1906). It is abundant in northern Illinois, 

 and passes into parts of Wisconsin and Minnesota, and also into eastern Nebraska. 

 But the exact boundaries in this region require further investigation. 



Lasmigona (Platynaias) subviridis (Conrad) (1835). 

 Sytnphynota viridis Simpson, 1914, p. 484; Lasmigona subviridis (Conard) Frier- 

 son, 1915, p. 58. 



Plate IX, figs. 3, 4. 



Records from Pennsylvania : 



Conrad, 18.36 (Schuylkill River, Philadelphia; Lancaster; Juniata River). 



Lea, 1838 (Juniata River, Hollidaysburg, Blair Co.). 



Haldeman, 1844 (Lancaster Co.). 



Conrad, 1856 (Schuj'lkill River, Phoenixville, Chester Co.; Delaware River, Morrisville, Bucks Co.: 



"opposite Trenton"). 

 Bruckhart, 1869 (Lancaster Co.). 



Hartman & Michener, 1874 (Schuylkill River, Chester Co.). 

 Marsh.all, 1895 (Juniata River and Philadelphia). 

 Ortmann, 19096, p. 206. 



Characters of the shell; Shell very much like that of L. viridis, but invariably 

 much smaller, thinner, and more delicate, with the hinge-teeth thin and weak. 

 The interdental projection of the left valve is quite rudimentarj', and generally, 

 no indication of it is present. The outline of the shell is not so distinctly trape- 

 zoidal, but rather subovate, narrower in front, higher behind, and the upper 

 margin forms only a blunt angle with the posterior margin. The two valves are 

 not so distinctly compressed, as in L. viridis, and the swelling in the region of the 

 posterior ridge is generally more pronounced, so that the whole shell appears 

 relatively more inflated. Beak-sculpture similar to that of L. viridis, but the 

 bars are stronger and less in number (four); they do not extend so far upon the 

 disk, are more equal, with the posterior loop not so sharply angled (See ISIarshall, 

 1890, p. 176, fig. 2). Epidermis yellowish brown to olive greenish, with more or 

 less distinct green rays, which are most distinct and crowded upon the posterior 

 slope, so that the latter generally appears darker green. Nacre white and iridescent, 

 but often with lurid or dirty salmon tints. 



