STANTON.] NERITID-&. 127 



PAEAPHOLAS? Sp. 



A bit of fossil wood collected in the Pugnellus sandstone of Poison 

 canyon, Colorado, contained several short tubes of a boring mollusk 

 that may belong to this genus. The large end of the tube is rounded 

 and it tapers rapidly toward the posterior end. It seems to be a much 

 shorter species than Parapholas sphenoideus. 



GASTROPODA. 



NERITID^E. 



Genus NERITINA Lamarck. 



Neritina pisum Meek. 



PL xxvin, Figs. 1-3. 



Neritina (Neritella) pisum and N. pisiformis Meek, 1873, Ann. Rept. U. S. Geol. Snr. 



Terr, for 1872, p. 500. 

 Neritina pisum White, 1879, idem for 1877, p. 308, PI. 7, Figs, lla-e. 

 Neritina pisiformis White, 1880, idem for 1878, p. 26, PI. 12, Figs. 9a-c. 



The original description of Neritina pisum is as follows : 



" Shell globose; spire much depressed; volutions about three, rapidly 

 increasing in size, so that the last or body turn (which is a little depressed 

 above) composes nearly the entire shell; inner lip broad, flattened, 

 and smooth; aperture small and semicircular; surface nearly or quite 

 smooth. 



" Height, 0.22 inch; breadth, 0.26 inch." 



On the same page the following description of Neritina pisiformis is 

 given : 



"Shell small, subglobose, or obliquely rhombic, the height being 

 slightly less than the oblique breadth; spire rather prominent for a 

 species of this genus; volutions three to three and a half; convex; last 

 one large, and forming most of the bulk of the shell; aperture subovate, 

 considerably contracted by the flattened, moderately wide inner lip, 

 which is nearly straight on its inner margin, and provided there with 

 four small denticles, the upper one of which is largest. Surface smooth. 



" Height, 0.30 inch ; greatest oblique breadth, 0.32 inch. 



" This little shell agrees so nearly in size and form with the described 

 species (N. pisum) that they may be readily confounded, as they are 

 found with the aperture filled with rock. A fortunate fracture of one 

 of the specimens exposed the inner edge of its flattened column ella, 

 however, and thus enabled me to see that it is denticulated, and in this 

 respect differs from Neritina pisum, which seems to be entirely without 

 teeth. Further comparisons also show the two sheHs to differ in form, 

 that under consideration having a more prominent spire and a more 

 globose outline, being less oblique." 



On attempting to separate collections from the typical locality into 



