MOLLUSCA OF MICHIGAN— WALKER. 47? 



Helix concava, Sager, Doc. H. Rep. Mich., 1839, 420, separate, 14. 



, Miles, Rep. Geol. Surv. Mich., 235, (1861). 



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



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



Selenites concavus, Walker, Rev. Moll. Fauna Mich., 16, (1894). 



Generally distributed south of the Saginaw-Grand Valley. North of that 

 it has only been reported from Lime island in the St. Mary's river. 



Superfamily AULACOPODA. 

 KEY TO THE FAMILIES OF AULACOPODA* 



I. Marginal teeth with narrow, lengthened basal plates, either unicuspid 



and thornlike or bicuspid by elevation of outer on middle cusps. 

 a. Foot-margin wide; shell more or less spiral, ovotestis imbedded in 



liver Zonitidce. 



aa. Foot-margin narrow; shell a thin internal plate, not spiral; ovotestis 



free from liver Limacidce. 



II. Marginal tooth with short, wide and squarish basal plates with one 



or several cusps, the outer cusp never elevated on middle cusp. 



a. Shell spiral, usually wholly external Endodontidoe. 



aa. No shell, mantle covering the whole upper surface Philoviycidce. 



Family ZONITID/E. 



Animal entirely covered with an external, more or less shining shell, with 

 or without caudal mucus-pore; foot-margin wide and sole frequently tripar- 

 tite, defined by a pedal groove; ovotestis imbedded in liver; marginal teeth 

 with narrow, elongated basal plates and either unicuspid and thorn-shaped 

 by suppression of side cusps, or bicuspid by elevation of outer on middle 

 cusps. 



KEY TO GENERA OF ZONITID^.^ 



I. ^System bearing a long dart-sack surmounted by one or more coronal 



glands, and usually containing a slender, curved dart. 

 a. Shell with internal teeth, or a layer of callus on the floor of last whorl 



Gastrodonta. 



aa. No internal teeth or callus. 



h. Surface polished or with minute spiral lines Zonitoides. 



hh. Surface conspicuously striate or constulate Pseudohyalina. 



II. ^System lacking dart-sack and its accessories. 



a. No noticeable shell-lobes developed, caudal mucus-pore present. 



h. Shell small depressed and glassy; lower part of vas deferens not 



enlarged Vitrea. 



hh. Shell larger, smoky; lower part of vas deferens greatly en- 

 larged Omphalina. 



aa. Right shell lobe developed ; no caudal pore Vitrina^ 



* Adapted from Pilsbrv, Naut. IX. 109. 

 t Adapted from Pilsbry, Naut. IX. 17. 



