MOLLUSCA OF MICHIGAN— WALKER. 515 



11. Outer lip strongly indented at its upper third. 



a. Shell oval or suboylindrical, last whorl not wider than the penul- 

 timate. 

 b. Last whorl scarcely higher and narrower than penultimate. Alt. 



2.7 mm morsei. 



hb. Last whorl nearly one-half entire length, wide as penultimate. Alt. 



2 mm gouldii. 



bob. Penultimate whorl widest, shell very minute. Alt. 4-5 mm. 



milium. 



aa. Shell ovate, conic, ventricose, last whorl widest. 



b. Larger, ventricose whorls 5, Alt. 2 mm ovata. 



bb. Smaller, sub-cylindrical, whorls 4, Alt. If mm ventricosa. 



Subgenus VERTILLA Moquin-Tandon. 



Shell minute, last w^horl narrow^ed toward the aperture, which is indented 

 by a deep constriction corresponding to the superior palatal fold, a long 

 gular fold connecting Avith one of the palatals and abruptly deflected at its 

 inner extremity, coliimellar lamella long, bulging in the centre and parallel 

 Avith the columella; inferior palatal smaller than the superior. 



Fig. 143. Arrangement of apertural folds in VertiUn. (Sterki.) 



a 



X17.5. 



VERTIGO MILIUM (Gould). 



Shell very minute, subcylindrical, diminishing 

 equally to both extremities; clark amber or chestnut 

 color; w^horls 5, rounded, very minutely striate; apex 

 obtuse; suture deep, peristome w-hite; aperture 

 within brownish, general shape semi-circular, trun- 

 cated above by the last w^horl, outer lip incurved in 

 the middle, lamellae 6-8, tw^o parietal, two columellar, 

 two palatal, the superior one large, lamellar, and 

 Fig. 147. V. miimrn. (Morse. )gj^^^p^y ^^^^ downward at its inner extremity. 



Alt. 4-5, diam. 2-5 mm. 

 Pupa milium, Gould, Bost. Jour. Nat. Hist. IIL, 402, pi. IIL, fig. 23, 

 (1840). 



Vertigo , W. G. Binney, Man. Am. Land Shells, 332, fig. 361, (1885). 



, Currier, Shell-bearing Moll. Mich., 6, (1865). 



, DeCamp, Shell-bearing Moll. Mich., 7, (1881). 



Pupa , Walker, Rev. Moll. Fauna Mich., 17, (1894). 



Rarely reported, probably on account of its small size. Reported from 

 New^aygo, Kent, Bay, Oakland, Washtena^v and Lenawee counties. 



Subgenus VERTIGO s. s. 



Palatal folds simple; no gular fold. 

 50 



