1896.] NATURAL SCIENCES OF PHILADELPHIA. 17 



P. matermontana is like texasiana in the notch between the two 

 lip-teeth, but the outer tooth is a more pronounced and shorter 

 lamella, the parietal " V " is less developed, and the upper surface 

 is not costalate. The parietal lamella is much alike in matermon- 

 tana and laUsjiira, the outer branch being much less developed than 

 in Ixichardsoni, veidrosula or bicru7-is. The umbilicus is like that of 

 latispira, being slightly more ample than in texasiana, and with 

 the central well, or perforation decidedly larger. 



This species and the three following have nearly the same 

 form of aperture teeth and are very similar to other species group- 

 ing immediately around P. ventrosula in this respect. The compar- 

 ative width of umbilicus, the sculpture, and to a less extent, the 

 contour, differ in the several forms. The inverted T shaped tooth 

 upon the outer lip, formed by a lamella parallel to the lip-edge with 

 a shorter one at its lower end, transverse to it, is characteristic of 

 the group. 



P. Ponsonbyi n. sp. PI. II. figs. 1, 2, .3. 



Shell globose-depressed, with low conoid-convex spire, rounded 

 periphery and convex base. Umbilicus one-sixth the diameter of 

 shell, with flattened, nearly vertical w^alls, narrowing to a perfora- 

 tion beyond the last whorl. Surface shilling, smooth except for 

 extremely faint growth-wrinkles ; corneous-brown, with a chestnut- 

 brown super-peripheral band on the body- whorl, appearing on the 

 spire as a narrow sutural margiuation. AVhorls 5?, convex, slowly 

 widening, the last decidedly wider, tumid on the latter half of the 

 base, deeply and narrowdy constricted behind the outer and basal 

 lips. Suture well and evenly impressed, abruptly and deeply 

 deflexed in front. 



Aperture very oblique, rounded-oval, the lip forming three-fourths 

 of the circumference. Outer lip broadly flaring, its inner edge bear- 

 ing a short concave lamella, with a projecting compressed tooth at 

 its lower end ; basal lip reflexed, with a similar compressed tooth. 

 Parietal wall bearing a short, erect, straight lamina parallel with 

 the basal lip, and having a very short V-branch at the outer end ; 

 the inner termination not extending to the columella insertion. 



Alt. 5, greatest diam. 8*2, lesser 7*2 mm. 



Types from Mexico, exact locality not known, in the collections 

 of John Ponsonby and the Academy of Natural Sciences of Philad. 



Like ventrosula and Richardsoni in the teeth of the lip, but more 

 globose than either, parietal tooth with only a trace of the outer 



