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 only a rudimentary shell, or shell wanting 

 entirely, pp.i29; 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. 110 



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 K inch or less in diameter. .. VALLONIIDAE, p. 116 

 Shell at least 34 inch in diameter, usually from )^ to 1 inch 



in diameter 6 



6. Whorls of spire not separated bv a suture 



.. ...HELICIXIDAE, p. 39 



Whorls of spire separated bv 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 ZOXITIDAE, p. 64 



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

 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 



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

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



11. Aperture without plications or denticulations of anv kind, 



p. 120... ..........' 12 



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



12. Shell yellowish, polished COCHLICOPIDAE, p. 120 



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



13. Aperture round; provided with denticulations 



PUPILLIDAE (part), p. 93 



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

 plait on parietal wall ELLOBIID.-\E, p. 135 



14. Mantle covering only anterior portion of body 



'. LIMACIDAE, p. 128 



Mantle almost or entirely covering body 



■ ^ PHI'LOMYCIDAE, p. 131 



