178 PROCEEDINGS OF THE ACADEMY OF 
subobsolete ribs near the cutting margin. In asterzscus there are 
coarse wrinkles, resembling subobsolete ribs. In perspectiva, 
striatella, and Idahoensis there are such wrinkles, and also coarse 
vertical striae. I have not found the strize as oblique as shown in 
fio. 20. In solitara, alternata, and Hemphilli there are no traces 
of either ribs, wrinkles or striz. In all these species there is a 
tendency to a median projection to the cutting edge. This is 
greatly developed in soliaria, alternata, and especially in Hemp- 
hill. The last two species have also a much more arcuate jaw 
than the others. I have not seen the jaw of Haydenit, Cumber- 
landiana,' tenuistriata, Horni, pauper, incrustata, or vortex. 
Patula is described by von Martens as having a ribbed jaw, 
which does not agree with my observations on the jaw of our 
North American species. As there appears considerable confusion 
in regard to the limits of the genus, I think it best to make no 
reference here to any species foreign to America. 
Fig. 22. 
Pes Ap er Ai Bier: a 
eReRAAE AG 
Lingual dentition of P. alternata. [Morse.] 
Fig. 22 shows the general arrangement of the teeth on the 
membrane. The characters of the individual teeth are better 
shown on my plate VII. 
There is considerable difference in the lingual dentition of the 
species I have grouped in this genus as to the development of the 
side cusps to the central and lateral teeth, and the presence of dis- 
1 T have lately received a specimen from University Place, Tenn., from 
Dr. Elliott. The jaw has very coarse perpendicular strie. 
