ORTMANN: monograph of the naiades of PENNSYLVANIA. 5 



the upper Lehigh-drainage, in the Pocono Mountains, and in the region of the 

 North Branch of the Susquehanna, but without success. 



In the upper Little SchuylkiU-drainage this species lives in mountain streams 

 with cold water (trout-streams) at an elevation of 800 feet and more above sea- 

 level. The sources of these streams are at about 2000 feet, and the greatest 

 number of shells is found at about 1000 to 1200 feet. These streams are rough 

 and full of little falls and rapids. The shell prefers eddies and pools which are 

 rather deep, with a steady and lively current, and with gravelly and sandy bottoms. 

 Sometimes these shells are found in sandy (but not muddy) bottoms of mill-ponds 

 in quiet water, but they probably have been washed down into these. Cold water 

 with lively currents seems to be essential, and also shade, for I chiefly found speci- 

 mens in places where the banks of the streams were wooded, and not where they 

 ran through open fields. The characteristic shrub in these woods is Rhododendron 

 maximum, and besides Alnus, Carpinus, and often Tsuga. 



In Europe it has been observed that Margaritana is missing in streams which 

 run over limestone rocks, and that it is very impatient of water which holds lime 

 (Haas, 1910, p. 109) . The same is true in this country. All the streams in Schuyl- 

 kill County in which it lives run over sandstones and shales. Indian Run is 

 entirely in the Devonian Clinton Shales, while Cold Run and the more northern 

 streams are in the Lower Carboniferous Mauch Chunk Shales, the boulders in the 

 water-courses being formed by sandstones and conglomerates of the overljdng 

 Pottsville beds.* 



The headwaters of the Little Schuylkill form a perfectly isolated station for 

 this species, about one hundred miles away from the nearest locality, which is 

 to the North, in Rockland County, in southern New York. The Pennsylvanian 

 area of this species is not only the most southern extension of its range in eastern 

 North America, but it also has the peculiarity of being the only one to the South 

 of the Terminal Moraine. Thus it may be regarded as a part of the Glacial Preserve 

 {refugium) of this species (See Ortmann, 1913a, pp. 377 fT.). Margaritana mar- 

 garitifera in Pennsylvania is a fine example of a Glacial ReUc.^ 



■< In this connection I should mention that O. 0. Nylander, who sent me specimens from the Aroos- 

 took River, Maine, states positively that the formation is Aroostook Limestone (Silurian. Cf. Williams, 

 H. S., & Gregory, H. E., in Bull. U. S. Geol. Surv., 165, 1900, pp. 44 and 141). This matter, however, 

 should be investigated more carefully. 



5 Subfossil shells of Margaritana margaritifcra have been found in Hartnian's Cave, near Strouds- 

 burg, Monroe Co., Pa., associated with shells of Elliptio violaceics {Unio complaiuitus), bones of living 

 and extinct vertebrates, and with human implements of stone, bone, and horn (See Leidy, 1SS9). I have 

 seen, in the Philadelphia Academy of Natural Sciences, a left valve taken from Hartman's CavC, which 

 undoubtedly is this species. This locality is wilhin tiie glaciated area, and thus these remains are surely 



