136 MEMOIRS OF THE CARNEGIE MUSEUM. 



are the environmental features, which have favored its estabhshment there. Fur- 

 thermore the question remains to be answered how it succeeded in reaching these 

 isolated stations. 



With regard to this phenomenon, attention may be called to the fact that this 

 species, although distributed over the whole state of Ohio (Sterki, 1907a), is especi- 

 ally found in its northeastern part, not far from the Pennsylvanian localities. 

 Dean reports it from Mahoning River; " Silver Creek, Portage Co.; and from 

 Cuyahoga River (lake-drainage). It seems that there might be here a connection 

 with the Pennsylvanian localities, and then this species very likely would belong 

 in the same category as Lasmigona viridis (see above). 



This species has a very wide distribution, and is found according to Simpson 

 (1900) in the "upper Mississippi-drainage as far south as Arkansas in the west; 

 Ohio River-system; upper St. Lawrence and its tributaries, north into Mackenzie 

 River." A number of localities are known in the Lake Winnipeg and Nelson 

 drainages; in Lake of the Woods belonging to the upper Lakes drainage. It 

 occurs also in Michigan (Walker, 1898) in the lake-drainage, and in Rouge River 

 at Detroit belonging to the Lake Erie-drainage. It is found in the Erie-drainage 

 in Indiana and Ohio (Goodrich, 1914, Dean), but it has never been reported from 

 Lake Erie proper (Walker, 1913, p. 22). A record from Buffalo cannot be credited 

 on account of the general inaccuracy of this list, and Call's "western New York" 

 remains unconfirmed (Marshall, 1895). In addition, it goes southward into the 

 Alabama-drainage, according to Cair(1885) and Lewis (1877) (See also specimens 

 in Carnegie Museum). Strangely enough localities from South of the Ohio in 

 Kentucky and Tennessee are not known, except the record of Wilson & Clark 

 (1914) from the Cumberland in Tennessee. Apparently, the Alabama localities 

 are connected with the rest of the range not in a northerly, but in a westerly direc- 

 tion. The species is found in northern Louisiana (Marshall, 1895; Vaughan, 1893). 

 It extends westward to Iowa, Kansas, Arkansas, and Oklahoma. 



Note: SiMPSONicoNCHA AMBiGUA (Say) (1825). 

 Hemilastena ambigua (Say) Simpson, 1914, p. 325.^^ 



This species has never been found in Pennsylvania. According to Simpson 

 it is distributed in the "Ohio River system; north to Michigan; west to Iowa; 

 south to Arkansas; east to Tennessee." According to Dean (1890), it is rare in 

 the Mahoning River, Ohio, but I have hunted for it in vain in the Pennsylvanian 

 part of this river. 



*' No trace of it in the Pennsylvanian part of this river. 



** As to the generic names Simpsonaias and Simpsoniconcha, see Frierson, 1914a, p. 7, and 19146, 

 p. 40. 



