HELIX. 



141 



Helix mitchelUana, Deshates in Fer. I, 137, pi. xcvii, f. 4-7, nee 13-1 b\ 

 Mesodon pennsylvanica, Tryon, Am. Journ. Conch. Ill, 44, pi. viii, f. 9 

 (1867). 



Western part of Pennsylvania, Ohio, Illinois, Kentucky. 



This species may be readily distiuguished from clausa and 

 mitchelUana by its somewhat triangular aperture, which is more 

 like that of H. elevata; it is more elevated, has usually six 

 whirls, more convex, and with deeper suture than in H. clausa. 

 In mature shells the inner margin of the peristome, near the 

 columella, has a tooth-like callus, very similar to that often pre- 

 vailing in forms of H. exoleta, ihyroides, and albolabris. The 

 umbilicus is invariably more or less open in H. clausa, 

 but closed in H. iminsylvanica and mitchelUana. 



Jaw very arcuate, of uniform width ; ends blunt ; 

 anterior surface with stout, crowded ribs, denticu- 

 lating either margin. 



Lingual membrane with 120 rows of 29 — 1 — 29 

 teeth each ; centrals short, broad, with a conical, 

 acutely-pointed middle cusp, and obsolete side-cusps; laterals 



Fig. 238. 



Jaw of 

 JJelix pennsyl- 

 vanica. 



Fig. 239. 



Lingnal dentition of Helix pennsylvanica. 



of same shape, but bicuspid ; uncini large, irregularly denticu- 

 lated. 



Cat. No. 



792.5 

 S042 

 8"in4 

 S767 



No.ofSp. 



Locality. 



Columbus, Ohio. 



From whom received. 



Dr. J. Lewis. 



W. G. Binnpy. 

 W. Stimpsoa. 



Kemarks. 



Helix mitclielliana, Lea.— Shell imrerforate.depressed-conoid- 

 globose, thin, with crowded strise and very crowded decussating microscopic 

 line.s pellucid, horn-color, polished ; spire briefly conoid ; whirls five, 

 moderately convex, gradually increasing, the last ventricose, snhcon- 

 stricted and briefly deflected anteriorly ; aperture diagonal, lunate, sub- 



