MOLLHSCA OF MICHIGAN— WALKER. 503 



.S. retusa Lea, and to retain the name of ohliqua for this form, hut siicli 

 usage cannot be supported by the recognized law of priority in nomenchiture. 



SUCCINEA AVARA Say. 



/r\ Shell rather small, very thin and fragile, yellowish horn-color, 



^A amber-colored or greenish; shining, minutely hirsute ;when young; 



\J whorls 3, very convex, separated by a *deep suture; last whorl 

 Fig. 114. large, not much expanded; spire very prominent, acute; aperture 

 (Binney') ovate, rounded at both extremities, about half as long as the shell . 



Alt.' 6-10 mm. 

 Succinea avara, Say, Long's Exped., II., 260, pi. XV., fig. 6, (1822). 



, W. G. Binney, Man. Am. Land Shells, 339, fig. 369, (1885). 



, Miles, Rep. Geol. Surv. Mich., (1861). 



, Currier, Shell-bearing Moll. Mich., 4, (1868). 



, DeCamp, Shell-bearing Moll. Mich., 5, (1881). 



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



Var. ALBA Cockerell. 



Shell white or greenish white. 



Succinea avara alba, Cockerell, Naut. VII., 43, (1893). 



Var. MAJOR W. G. Binney. 



Larger, Alt. 10-14 mm. 



Succinea avara major, W. G. Binney, Proc. A. N. S. P., 1858, 199. 



Var. VERMETA Say. 



Succinea vermeta, Say, New Harm. Diss., II., 230, (1829). 



, Miles, Rep. Geol. Surv. Mich., 236, (1861). 



, Currier, Shell-bearing Moll. Mich., 4, (1865). 



, DeCamp, Shell-bearing Moll. Mich., 5, (1881). 



Suture very deeply impressed, almost scalariform. 



Very abundant and of general distribution. The varieties major and 

 vermeta occur quite frequently associated with the type and intergrade 

 completely with it and with each other. The var. alba is more rare. 

 Two or even all of the varietal characteristics may be not uncommonly 

 found exemplified in a single individual. 



III. ORTHURETHRA. 



KEY TO THE FAMILIES OF ORTHURETHRA. 



I. Shell elongated, subcylindrical. 



a. Columella truncated Cochlicopidce. 



aa. Columella continuous with the basal lip PwpillidcE. 



II. Shell conical, heliciform. 



a. Aperture with parietal lamellse Pupillidce. 



aa. No apertural lamellse Valloniidce. 



