78 POLYGYRA-POLYGYRELLA. 



Jaw having the ribs wide and rather more crowded than is usual 

 in the other sections of the genus (pi. 31, fig. 25. P. monodon). 



Radula having ectocones developed on all the teeth ; basal plates 

 short and square, slightly shorter than the mesocones of central and 

 lateral teeth ; marginals with the basal plates short, wide, mesocone 

 bluntly bifid at tip, ectocone simple or bluntly bifid (pi. 31, fig. 26, 

 P. hirsuta). 



Distribution: Entire Gulf and Atlantic drainages, north to 

 Canada and south to southern Texas (San Antonio) ; Oregon'. The 

 species live under and around decaying logs and bits of wood. 



This is a well-marked section, distinguished by the compact nar- 

 row-mouthed shell as well as the crowded, wide ribs of the jaw. The 

 hairs of the shell collect a coat of earth, which renders the snails 

 difficult to see, the dusky shade of the animal also assimilating their 

 color to the surrounding earth or rotten wood. P. monodon ranges 

 over nearly all of eastern North America ; P. hirsuta has almost as 

 wide a distribution ; but the other species are rarer and more local ; 

 P. maxillata, bar big era, edvardsi, edgariana, labrosa and spinosa 

 being confined to certain localities in the Cumberland system of 

 mountains. P. germana is ( found in Oregon, but it may prove 

 related to the mullani group of Triodopsis, rather than to Stenotrema. 



Species of Stenotrema. 



HP. spinosa Lea, iii, 141. P. hirsuta Say, iii, 140. 



P. labrosa Bid., iii, 141. f porcina Say. 



P. edgariana Lea, iii, 141. v. altispira Pils. 



P. edvardsi Bid., iii, 141. P. maxillata Old., iii, 141. 



P. barbigera Redf., iii, 142. ^ P. monodon Rack., iii, 142. 

 -P. Stenotrema Fer., iii, 140. v. fraterna Say, iii, 142. 



hirsuta var. a. Fer. v. alicise Pils., viii, 152. 



convexa Raf. v. cincta Lewis, viii, 152. 



v. subglobosa Pils., viii, 152. P. leai Ward, iii, 142. 



P. germana Old., iii, 143. 



Genus POLYGYRELLA Binney, 1863. 

 =Polygyrella Binn. & J$ld.-t-Ammonitella Cooper. 



Shell discoidal, openly umbilicated, the spire slightly convex, flat, 

 or concave; texture glassy, somewhat translucent. Aperture sub- 



