134 ELEVENTH REPORT. 



KEY TO THE GENERA OF GASTROPODA OF MICHIGAN. 



H. BURRINGTON BaKER. 



This key is a purely artificial one and is based mainly on the shape of the 

 shells. Characters varying with age are excluded, in so far as possible, but 

 it was found impossible to make a key that would positively identify young 

 shells; these, however, the student will soon learn to recognize. Technical 

 terras have been used as little as possible; those used are explained in the 

 glossary. 



The key begins by dividing the gastropods into two groups; those without 

 shells and those with them. The latter are subdivided into six divisions: 

 heliciform, planorbiform, lymnaeiform, pupiform, turretiform, and patelli- 

 form shells. These divisions are made on the shape of the shell and will 

 be understood upon examining the illustrations. In cases where a shell 

 might be included under more than one head, this has been done. 



The illustrations are printed through the generosity of Mr. Bryant Walker, 

 who provided the plates. An example of each genus is given, and the number 

 after each indicates the number of diameters the drawing is magnified. In 

 preparing this key, use has been made of Mr. Bryant Walker's' and Mr. 

 F. C. Baker's^ papers. The student is refered to them for settling doubtful 

 points. 



Animal with no visible shell, i. e. slugs 1 



Animal with a visible shell, i. e. snails 3 



1. Animal with internal shell; mantle covering only 



anterior part of slug Agriolimax 



Animal Avithout internal shell; mantle covering all of ^^i^^ 



animal 2 a. campestris (Say)3 xi. 



2. Animal large ; adults ^^^?^^^^^t^^.f5^^^^^^^^r^?; ^ 



PhilotniJCUS. p. caioUnensis (Bosc) XI- 



Animals small; adults 2.5 c. m. long, un- 

 spotted PaUijera. 



p. hemphilli (W. G. Binney) XI. 



3. Shell heliciform, broader than high 4 



Shell planorbiform, spire not above last whorl 18 



Shell lymnaeiform, higher than broad, with an acute apex 20 



Shell pupiform, higher than broad, with a rounded a]3ex, aperture 



transverse .' 32 



Shell turretiform, conical, with almost straight sides 40 



Shell patelliform, with no coiled spire 42 



4. Shell operculated, with continuous peristome, small, 7 mm. high . . 5 

 Shell not operculated, peristome not continuous 6 



'Geological Surv. of Mich , Ann. Kept. 1905. 

 2Chicago Acad, of Sci , Bull.. Ill of xMat. Hist. Siiivey 



=The names of authorities are all inchifled in parentheses whetluT lliat aiil iKirity used 

 the generic name or not. 



