1894.] XATURAL SCIENCES OF PHILADELPHIA. 19 



phia specimeus, tliese have a wide range of variation in size and de- 

 gree of closure of the umbilicus. Seven out of the nine adults pre- 

 served from Cumberland, have developed a strong parietal tooth. 

 Collected l)y Stone at York Furnace, York Co., Pa. 



P. albolabris .Say. 



■Monterey, Franklin Co., Pa., 64,707, large (31 mm. diam.), 

 solid and dark colored. Cave Town, Washington Co., INld., 64,708, 

 small, (26 to 28 nun. diam. ) and solid. Fairview, top of North 

 Mountain, Md. Foothills, 64,706, and summit, 64,709, of Martin's 

 Mt, Allegheny Co., Md., small specimens. Cumberland, Md., 

 64,710, large and solid, measuring o2 mm. diameter. West Vir- 

 ginia, opposite Hancock, Md. 



It is curious to note that the specimens from Franklin Co., Pa., 

 collected in a porphyritic region, should markedly exceed in size those 

 from Cave Town and ^lartiu's Mountain, Md., tracts rich in lime- 

 stone, the soil being mainly formed by its disintegration. The small- 

 est specimens (22 mm. diam.) were collected at the foot of Martin's 

 Mountain. Stone collected this species at York Furnace, York 

 Co., Pa. 



P. palliata Say. 



Cund)erland, Md., 68,710, typical. Collected also by Stone at 

 York Furnace, York Co. , Pa. , where lie found it only in hemlock 

 woods. In the Catskill Mountains I have found it under the loose 

 bark of iallen hemlock boles. 



P. tridentata Say. PI. 1, Fig. 7. 



Cundierland, Md. , 64,714. Typical specimens in every respect, 

 measuring 13 mm. in diameter. Also found in Morgan Co., W. 

 Va., opposite Hancock, 64,715. In both localities associated with 

 P. fraudidenta. 



It must be distinctly understood that Say's types of this species 

 were the small forms found in the " Middle States." Say describes 

 it as " half an inch wide." He afterward collected the large form 

 in the Ohio basin, referring it to the same species. This large form 

 should be regarded as a geographic race. In Terr. Moll., Ill, the 

 typical form is figured on PI. XXVII, side figures, and the large 

 race is shown in the upper, lower and central figures of the same 



