20 PROCEEDTNGS OF THE ACADEMY OF [1894. 



plate. Bin ney's wood -cuts (Man. Amer. L. Sh. etc.) represent the 

 large form from Ohio. 



P. tridentata juxtidens n. vur. PI. 1, Fig:, s. 



Cave Town, Md., 64,720; very numerous in stony places. This 

 is a limestone region, and the red soil is largely the result of lime- 

 stone decomposition. The same foi-m of Triodopsis was found at 

 Gettysburg, Pa., 64,719, and in Allegheny Co., Md. , between 

 Green and Polish Mountains, 64,716, Chewsville, Md. , 64,717, at 

 Fairview, summit of North Mountain, Md., and in Morgan Co., W. 

 Va., opposite Hancock, 64,718. It is common around Philadelphia, 

 where typical tridentata also occurs. 



This form is distinguished from typical tridentata by the lower 

 position of the upi)er lip-tooth, the latter part of the parietal 

 lamella being directed toward this tooth or to a point above 

 it, whilst in the type the lip-teeth are more separated and 

 the latter portion of the parietal lamella is directed toward a 

 point on the peristome between them. The variety is more coarsely 

 striated also. The number of whorls (5) is the same in variety and 

 type. The measurements of three individuals are as follows : 



Alt. 7 diam. 14 mm. (Philadelphia). 



G'i " 13^ " (Cave Town, Md., largest). 

 6 " 11 " ( " " " smallest). 



The upper lip-tooth is sometimes broader than the lower, and oc- 

 casionally a trifle "inflected." The parietal blade is slightly 

 arcuate. 



P. tridentata fraudulenta u. var. PI. 1. Fig. 6. 



Morgan Co., W. Va. , opposite Hancock, Md., 64,724 and 

 64,725; Cumberland, Md., 64,723. At both of these localities it 

 is found living with typical P. tridentata. 



In its typical development this vainety is a compact shell of a red- 

 dish-brown color (varying to white in some localities); the spire is 

 low-convex, composed of six closely coiled whorls, the last being nota- 

 bly deflexed in front and strongly constricted behind the lip. The 

 aperture is strongly "dished" or basin-shaped; the outer lip bears a 

 broad tongue-shaped inflected tooth, situated at the position of the 

 periphery of the shell. The middle of the basal lip bears a small 

 stpiarish tubercle, which is often laterally compressed. The parietal 



