336 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



a deep groove behind it ; aperture vrcW rounded, semicircular, considerably 

 contracted by the impressed groove behind the {)eristome, and a corresponding 

 testaceous deposit, or rib, within ; umbilicus small, round, not expanded ; um- 

 bilical region not impressed; base convex. Greater diameter 8, lesser 7 mill.; 

 height 4^ mill. 



Helix jejuna, Say, Journ. Phila. Acad., II. 158 (1821); Binney's ed., 9. — De 

 Kay, N. Y. Moll., 46. — Pfeiffeu, Mon. Hel. Viv., I. 147. — Bland, Ann. 

 N. Y. Lye, VI. 341 (1858). —W. G. Binney, Terr. Moll., IV. 67. 

 ffygromia jejuna, Thyon, Am. Journ. Conch., II. 308 (1866). 



A species of the Florida Subregion, found originally near Jacksonville, Flor- 

 ida,^ received by me from Indian River and St. Augustine, Florida, and noticed 

 as far north as Savannah, Georgia. 



Animal dirty white, neck darker, eye-peduncles black, — not quite twice the 

 breadth of the shell, — foot pointed. 



Nearly allied to M. Mohiliana ((|. v.), with which it is confounded in Vol. 11. 



Jaw, lingual dentition, and genitalia unknown. 



Mesodon Mobiliana, Lea. 



Shell globose, perforated, thin, smooth, with very delicate incremental striae, 

 horn-colored ; whorls 6, convex ; suture impressed, last whorl tumid below, glo- 

 bose, slightly descending, deeply constricted behind the peri- 

 stome, umbilical region scarcely excavated ; apex obtuse ; spire 

 elevated; aperture oblique, rounded; peristome thickened, white, 

 reflected, its terminations distant, that of the columellar some- 

 what concealing the perforation. Greater diameter 8|, lesser 6 



M. Mobiliana. ^[\l | height, 5 mill. 



Helix Mobiliana, Lea, Proc. Am. Phil. Soc, II. 82 (1841) ; Trans. Am. Phil. 

 Soc, IX. 17 ; Obs., IV. 17 (1844) ; in Troschel, Arch. f. Nat. 1843, II. 124. 

 — Pfeiffeu, Mon. Hel. Viv., I. 323; IV. 122. —Binney, Terr. Moll., II. 

 172, PL XLII, Fig. 2, part. 



A species of the Southern Region, received from near Mobile, and from 

 Baldwin, Florida. 



It has heretofore been confounded with M. Jejuna (q. v.). It must be 

 borne in mind that the figures in Terr. Moll., PI. XLII. Fig. 2, and Land 

 and Fresh-water Shells, Fig. 258, are of Jejuna, and do not represent Lea's 

 species. 



In M. Mobiliana there are 6 whorls ; the last whorl is remarkably constricted 

 and o-ibbous at the aperture, more tumid at the base and with smaller umbilicus 

 than in Jejuna. Tlie microscopic spiral lines on the embryonic whorls of the 

 latter are absent in the former. The peristome at its junction with the penul- 



1 The Cow Ford (not Cowfort) of the St. John's River, given by Mr. Say as the original 

 locality. 



