1909.] NATURAL SCIENCES OF PHILADELPHIA. 543 



tress above and joined to the outer lip-tooth, basal lip with one or two 



teeth. The following species belong here: 



P. plagioglossa (Ph.) P. guadalajarensis Pils. 



P. suprazonata Pils. P. bicruris (Pfr.) 



P. couloni (Shuttl.) P. matermontana Pils. 



P. richardsoni Marts. P. mat. jaliscoensis Pils. 



P. richardsoni lingualis Pils. P. nelsoni Dall. 



P. ponsonbyi Pils. P. nelsoni collisella Dall. 



P. ventrosula (Pfr.) P. euglypta Pils. 



P. ventrosula hindsi (Pfr.) P. albicostulata Pils. 



Of these forms I have not seen P. bicruris and P couloni, or typical 

 specimens of P. ventrosula or richardsoni. 



This group of species is especially developed in western and northern 

 Mexico. Towards the southeast it is in large measure superseded by 

 the group of P. yucatanea, of which P. helictomphala is a common form. 

 In this group there is no distinct plate or buttress above the outer lip- 

 tooth, and the parietal tooth is reduced. 



Northward, the group of P. texasiana replaces the ventrosula group. 

 P. texasiana, P. triodontoides, P. mooreana, P. latispira and their 

 subspecies compose the texasiana group. 



The old records, on Sowerby's authority, of P. ventrosula and hindsi 

 from Texas must be erroneous. P. ariadnce, which forms another 

 group somewhat related to that of ventrosula, has been reported from 

 Texas, but it certainly has not been collected there recently. 



Polygyra oppilata implicata 'Beck' Martens. 



This is a common snail in the Panuco River basin. Dead shells are 

 abundant in river debris at Tampico. Living shells were found by 

 Mr. Hinkley inland. P. implicata has usually been ranked as a dis- 

 tinct species, but it differs from oppilata in only trifling details. When 

 fresh the shell is sparsely hairy. 



Mingled with implicata in the river debris, but probably from separate 

 localities or stations, there are specimens in which the upper angle 

 of the peristome is built out from the whorl, somewhat as in P. auricu- 

 lata; the two lip-teeth are slightly more developed, the space between 

 them being narrower. This form I have called P. o. complicata. 



P. oppilata has been reported from Florida ( Shuttl eworth), at Cedar 

 Keys (W. G. Binney) ; but some similar form of P. postelliana must 

 have been mistaken for it. Of about the same size, and belonging 

 to a closely related group of species, such a mistake might easily be 

 made. 



The Mexican group of P. ariadnce is composed of species in which 



