324 MEMOIRS OF THE CARNEGIE MUSEUM, 



the shell-banks, among other bed-forming species. But here also it is not very 

 frequent, and the shell-heaps of the clam-diggers contain only small numbers. 

 These conditions remain the same all the way down to Portsmouth. Every 

 specimen found by myself has been taken, but the total sum collected from the 

 Ohio below Pennsj'lvania hardly amounts to two dozen. 



General distribution: Type locality, Muskingum River, Marietta, Washington 

 Co., Ohio (Hildreth). 



This species is found extending from western Pennsylvania down the Ohio 

 in the states of West Virginia, Ohio (Sterki, 1907a), Indiana (Call, 1896a), and 

 probablj' also Illinois and Kentucky. In the upper parts of the Ohio-drainage it 

 hardly goes into the tributaries. The type locality, Muskingum River, has re- 

 mained so far the only tributary, which contains it in Ohio. In Indiana it is also 

 found in the Wabash and White Rivers (Say, 1817, Call, 1896a and 1900), and in 

 Illinois (Baker, 1906) it is in the Wabash and in the Illinois River (as far up as 

 La SaUe Co.). It is in the Mississippi River in Illinois as well as in Iowa (Daven- 

 port, Scott Co.) according to Pratt (1876). Simpson (1900) says that it ascends 

 the Mississippi to Minnesota, but it has not been reported by Grant (1886) and 

 Holzinger (1888), and is not reported from Wisconsin by Lapham (1860). 



From the southern tributaries of the Ohio it is known from the Cumberland 

 River (Call, 1885; Simpson, 1900; Wilson & Clark, 1914) and in the Tennessee, it 

 goes up to the Clinch River in Anderson Co., Tennessee. 



West of the Mississippi previous records are scarce or doubtful. While Call 

 (1885) gives this species from Blue River in Kansas, Scammon (1906) records 

 L. higginsi for this river. The latter species, according to Simpson, is found 

 from the (probably lower) Ohio west to Iowa and southwest to Kansas.^"^ How- 

 ever, specimens sent to me by H. E. Wheeler from Ouachita River in Arkansas are 

 undoubtedly L. orhiculata, and thus the latter certainly goes southward to the 

 Ouachita River. Specimens from Black River, however, distinctly incline toward 

 higginsi. Utterback (1916) has only higginsi from Missouri, but not orhiculata. 



It is quite possible that L. higginsi is merely a local form of L. orhiculata, 

 the form of very large rivers with muddy bottoms. We have repeatedly seen in 

 other species that inflation of the beaks is a character of big-river-forms. If this is 

 another case of this kind, the relation of the Ouachita and Black River orhiculata 

 to that of the Ohio could be explained as that of an ecological race. Of course, 

 additional material should be studied. That there might be intergrades is indi- 

 cated by our specimens from Muscatine, which incline somewhat toward higginsi 



2°' As far as I can see L. higginsi (Lea) differs from L. orbiculata chiefly in the more inflated and 

 more elevated beaks, and in the color of the epidermis, wliich has more green in it. 



