194 MEMOIRS OF THE CARNEGIE MUSEUM. 



prefers strong currents and gravelly bottoms, thus being most frequently found 

 in and near riffles. In the mountains it goes far up into the headwaters, and the 

 most western locality is in Indiana Co., in a tributary of the West Branch of the 

 Susquehanna (Cush Cushion Creek). 



General distribution. Type locality, Schuylkill River, Philadelphia (Lamarck) . 



According to Simpson (1900), this species extends over the Atlantic-drainage 

 from the lower St. Lawrence to South Carolina. 



As has been stated above, the mutual relations of A. varicosa and marginata 

 'm central and western New York are doubtful, and specimens from New York 

 are generally recorded under the name of marginata, although it is beyond doubt, 

 according to our material, that varicosa is found in the upper Susquehanna-drainage 

 in New York, and, according to the figures of DeKay in other parts of the state also. 



The species has been reported from Maine (Lermond, 1909), New Hampshire 

 (Call), Massachusetts (Gould-Binney, 1870), Rhode Island (Carpenter, 1890), 

 and Connecticut (Linsley, 1845) but Johnson (1915, p. 27) erroneously calls the 

 New England form A. marginata. Southward from Pennsylvania, A. varicosa is 

 known from Red Clay Creek, Christiania Township, Newcastle Co., Delaware 

 (Rhoads, 1904), and from the Potomac-drainage, in addition to the localities repre- 

 sented in the Carnegie Museum, from Sideling Creek, AUegany Co., Maryland, 

 the Potomac River, Cherry Run, Morgan Co., West Virginia (Pilsbry, 1894). 



Farther South, exact localities are missing, but Simpson's statement, that 

 it extends to South Carolina, is substantiated by specimens collected by myself in 

 the upper Catawba River in North Carolina. Among the latter are individuals 

 which fully agree with the Pennsylvanian form, but this set is extremely variable 

 in shape and especially in color. 



A. varicosa of the Atlantic slope is the representant of the western A. mar- 

 ginata, and in its distribution apparently falls in line with several other Atlantic 

 species, constituting a northern stock in the fauna of the Atlantic slope. This 

 has been discussed elsewhere (Ortmann, 1913a, p. 363 & 370). 



Walker (1913, p. 22) reports this species from Lake Erie; this, however, re- 

 quires renewed attention, since the form from Lake Erie may belong to A. mar- 

 ginata (see above). I have never seen the lake-form, and thus I am miable to 

 judge. 



