178 



PROCEEDINGS OF THE ACADEMY OF 



subobsolete ribs near the cutting margin. In asteriscus there are 

 coarse wrinkles, resembling subobsolete ribs. In perspectiva, 

 striatella, and Idahoensis there are such wrinkles, and also coarse 

 vertical stria?. I have not found the striae as oblique as shown in 

 fig. 20. In solitara, alternata, and Hemphilli there are no traces 

 of either ribs, wrinkles or striae. In all tiiese species there is a 

 tendenc} r to a median projection to the cutting edge. This is 

 greatly developed in solilaria, alternate/,, and especially in Hemp- 

 hilli. The last two species have also a much more arcuate jaw 

 than the others. I have not seen the jaw of Haydeni, Cumber- 

 landianaj 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. 



Lingual dentition of P. alternata, [Morce] 



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 I have lately received a specimen from University Place, Tenn., from 

 Dr. Elliott. The jaw has very coarse perpendicular stria?. 



