192 MEMOIRS OF THE CARNEGIE MUSEUM. 



Breeding begins in August, when eggs are present; later, in September, glo- 

 chidia are found. These are carried over the winter, and are still in the marsupium 

 in May; discharge has been observed on May 3. 



This species supplements somewhat the incomplete observations on A. mar- 

 ginata, and probably the breeding seasons of both species are about identical. . 



Remarks: This species has been frequently misimderstood, and confused with 

 the western A. marginata. But Simpson (1900) (following Wright) recognized 

 its specific distinctness, and I now hold the same opinion, although formerly 

 (Ortmann, 19096) I regarded it as a variety of A. ynarginata. But this was before 

 I had realized that there is in the Susquehanna-drainage another form, which 

 actually is more closely related to A. marginata. 



A. varicosa is easily distinguished from A. marginata by the size and shape 

 of the shell, and from the var. marginata Susquehanna; it also differs in color. It is 

 generally much smaller than either of them, and specimens over 60 or 65 mm. in 

 length are quite scarce. 



Although there is much variation in shape and color, this species hardly ever 

 inclines toward the western form, and no intergrades are found. I possess only a 

 single individual (dead shell) from White Clay Creek, Avondale, Chester Co., 

 which has a sharper posterior ridge, and a lighter posterior slope, thus inclining 

 toward the var. susquehannce, but it has the general outline of varicosa, and, like 

 this, no spots. Being the only individual found at that locality, we cannot draw 

 any conclusions from it. 



In the Susquehanna-drainage, I repeatedly found this species associated with 

 A. marginata susqueJiannce, but had never any difficulty in separating them. That 

 there are two distinguishable forms in this region, was evident to me when I col- 

 lected them together for the first time (Ardenheim, Aug. 13, 1908), and further 

 study has only confirmed this view, although for a time I followed the views of 

 previous authors. 



Localities in Pennsylvania, represented in the Carnegie Museum: 



Delaware-drainage : 



Delaware River, Shawnee, Monroe Co.; Northampton Co. (G. W. Caffrcy coll., G. H. Clapp donor); 



Yardley, Bucks Co. 

 White Clay Creek, Avondale, Chester Co. 

 Ridley Creek, Delaware Co. (C. H. Conner). 



Leliigh River, Bethlehem, Northampton Co. (Holland collection). 

 Princess Creek, Kunkletown, Monroe Co. 

 Lizard Creek, Mantz, Schuylkill Co. 

 Mahoning Creek, Lehighton, Carbon Co. 



