38 ILLINOIS NATURAL HISTORY SURVEY MANUAL 



KEY TO FAMILIES 



1. Animal having a well-developed spiral shell into which it can 



withdraw, p. 40 (Snail) 2 



Animal having onlv a rudimentary shell, or shell wanting 

 entirely, pp. 129,' 131 (Slug) . . . .' 14 



2. Parietal wall of shell with plaits extending far back into 



whorl and with one or two plaits emerging from aperture 



STROBILOPSIDAE, p. 1 10 



Parietal wall of shell not with plaits extending far back into 

 whorl and emerging from aperture, pp. 39, 44 3 



3. Shell broader than high, spire flat or dome shaped, pp. 49, 92. .4 

 Shell higher than broad, spire pointed or elongate, pp. 96, 122.9 



4. Shell with lip reflected or turned back, edge thickened, p. 40. ,5 

 Shell with lip not reflected or turned back, edge sharp, p. 83. . 7 



5. Shell Vs inch or less in diameter. .. VALLONIIDAE, p. 116 

 Shell at least 3^ inch in diameter, usually from 3^ to 1 inch 



in diameter 6 



6. Whorls of spire not separated bv a suture 



HELICINIDAE, p. 39 



Whorls of spire separated by a distinct suture 



POLYGYRIDAE, p. 40 



7. Surface of shell dull, coarsely ribbed . ENDODONTI DAE, p. 83- 

 Surface of shell polished, smooth, p. 70 8 



8. Spire more or less rounded, p. 66; vitreous, with umbilicus 



relatively small .ZONITIDAE, p. 64' 



Spire flattened, p. 92; not vitreous, with umbilicus very 

 wide HAPLOTREMATIDAE, p. 91 



9. Aperture occupying one-half or more length of shell, p. 122 .. 10 

 Aperture occupying not more than one-third length of shell, 



p. 96 11 



.0. Shell with brown markings on surface . . BULIMULIDAE, p. 63 

 Shell with surface yellowish, unmarked. SUCCINEIDAE, p. 121 



LI. Aperture without plications or denticulations of any kind, 



p. 120 12 



Aperture with 1 or more plications or denticulations, p. 136. . 13 



[2. Shell yellowish, polished COCHLICOPIDAE, p. 120 



Shell brown, dull PUPILLIDAE (part), p. 93. 



[3. Aperture round; provided with denticulations 



PUPILLIDAE (part), p. 93 



Aperture long and narrow, p. 136; provided with a single 

 plait on parietal wall ELLOBIIDAE, p. 135 



[4. Mantle covering only anterior portion of body 



LIMACIDAE, p. 128 



Mantle almost or entirely covering body 



PHILOMtCIDAE, p. 131 



