MESODON. 323 



presence does not seem to cause any uneasiness, nor even to be felt by the 

 snail. 1 



Mesodon Mitchelliana, Lea. 

 Vol. III. PI. IV. outline figs. 



Shell imperforate, depressed conoid-globose, thin, with crowded stria?, and 

 very crowded decussating microscopic lines, pellucid, horn-color, polished ; spire 

 briefly conoid ; whorls 5, moderately convex, gradually increasing, the last ven- 

 tricose, subconstricted and briefly deflected anteriorly; aperture diagonal, lunate, 

 sub-pearleaceous within ; peristome white, thickened, its terminations slightly 

 converging, subequally reflected, that of the columella narrow, adherent, or 

 subdilated and spreading. Greater diameter 16|, lesser 14| mill.; height, 

 10 mill. 



Helix Mitchelliana, Lea, Am. Phil. Trans., VI. 87, PI. XXIII. Fig. 71 ; Obs., 

 II. 87 (1839); Troschel, Arch. f. Nat., 1839, II. 221. — DeKay, N. Y. 

 Moll., 45 (1843). — Pfeiffer, Mon. Hel. Viv., I. 291 ; IV. 322. — Bland, 

 Ann. N. Y. Lye, VI. 339 (1858). — W. G. Binney, Terr. Moll., IV. 47 ; L. & 

 Fr.-W. Sh., I. 141 (1869). 



Helix clausa, Binney, Terr. Moll., II. 109 ; in Vol. III. PI. IV., outline figures. 



Mesodon Mitchelliana, Tryon, Am. Journ. Conch., III. 45 (1867). 



Kentucky and Ohio, along the Ohio River; Munroe County, Virginia; 

 Cherokee Count; , North Carolina. A species of the Interior Region. 



In M. clausa the umbilical region is more widely excavated, and tie groove 

 behind the reflec ed peristome producing the contraction of the aperture, is 

 continued at die ba.se of the shell, becoming wider as it joins the umbilical 

 'ma the groove is almost obliterated at the point of 

 reflection i ' -tome over the umbilicus, by the more tumid character of 



the last wl 



Jaw arcuate, of uniform width throughout; ends blunt: anterior surface with 

 12 cro . ril ., <■ .'■ ul ting either margin. 



Lingua! membrane (PI. VIII. Fig. H) with 49 — 1 — 49 teeth; 18 lai 

 Outer laterals 1 i cusp ing points. 



The genital system is long and narrow. The oviduct ii g ,. 



The penis sac ; s Ions st »ut ylindrical, with a bulb-like « pansi 

 at which point both i I rens and retractor musch a insei 



genitn.' bla Ider i I rate, not much larger than its ict, . tch s 



short, and enter the I niddle of its length (PI. XL Fig. ' 



' ■■• > ■ •''!:' i ■ I nearly colorless or ' yj '. 



'- ■ des imp ised 7 ji 0.4 millin *' M* ***«» 



Differs in outline from which it respmliles in 



i appearance, m de of life, and in the large pair of projecting 

 setae anteriorly a orly. A colored line lias been ob- 



served. 



