ORTMANN: monograph of the naiades op PENNSYLVANIA. 103 



The only tributary of Lake Erie in Pennsylvania, Conneaut Creek, contains a 

 small race of typical E. dilatatus. There are no indications, that this has come 

 up from the lake. It may as well have crossed over from the Beaver or French 

 Creek drainages. 



Of course E. dilatatus sterkii must have come into the lake from the Ohio 

 system, and the Wabash-Maumee route is the first to be considered (See Walker, 

 1913), but it may have crossed elsewhere, since the typical form ascends in many 

 places far into the headwaters. The remarkable thing is that in all tributaries of 

 the lake the normal dilatatus is present, in Michigan at Ann Arbor), Marshall, 

 1895) in Ohio in the Cuyahoga (Dean, 1890) in Indiana in the drainage of the 

 Maumee, St. IMarys, and St. Josephs Rivers (Call, 1900). Call mentions the fact 

 that there is in the lakes of northern Indiana, a form which is flatter and thinner. 

 This, of course, would not lead to sterkii. 



Elliptio VIOLA ceus (Spengler) (1793). 



Unto violaceus Spengler. Haas, 1913, p. 54, text-fig. 2; Unio com-planalus 

 (Dillwyn) Simpson, 1914, p. 651. 



Plate VIII, figs. 4, 5. 

 Records from Pennsylvania: 



Say, 1817 (Delaware and Schuylkill Rivers) as purpweus (See Binney, 1858). 



Haldeman, 1844 (Lancaster Co.). 



Lea, Obs. IV, 1848 (Cobbs Creek, La Grange, near Philadelphia) (JuUginosus).^ 



Gabb, 1861 (League Island and Schuylkill River, Philadelphia). 



Bruckhart, 1869 (Lancaster Co.). 



Hartman & Michener, 1874 (Chester Co.). 



Schick, 1895 (Delaware and Schuylkill Rivers, Corinthian Reservoir, Philadelpliia; Canal at Manayunk, 



Philadelphia Co.; Munckinipattus Creek, Glenolden, Delaware Co.). 

 Ortmann, 19096, p. 208. 

 Caffrey, 1911 (Lehigh and Delaware Rivers, Northampton Co.). 



Characters of the shell: Shell moderately large and moderately heavy. Outline 

 subtrapezoidal, more or less elongate, generally almost twice as long as high, or 

 even longer. Anterior end rounded, posterior end slightl}' produced and slightly 

 pointed; lower margin more or less convex, often nearly straight. Upper margin 

 subparallel to the lower margin, forming an angle with the obliquely descending 

 posterior margin. Beaks not prominent, at variable distance from the anterior 

 end, but not close to it. Beak-sculpture distinct, consisting of five to six ridges, 

 the first two or three curved and subconcentric, those following running in the 



^ Cobbs Creek is a branch of Darby Creek, near Essington, Philadelphia County. 



