22 ILLINOIS NATURAL HISTORY SURVEY MANU/ 



pertinent, and we have provided devices known as keys^ frc 

 which a species may be identified by certain characteristics 

 combinations of characteristics that are peculiar to it. 



Key to the families. — Suppose you have found a lar. 

 snail with brown color bands encircling its coarsely ribbed, dom 

 shaped shell. You first consult the key to families on page 3 

 Under 1 you find, "Animal having a well-developed spiral sh< 

 into which it can withdraw," and "Animal having only a rue 

 mentary shell, or shell wanting entirely." The shell is spir 

 and well-developed; so you consult both parts of couplet 

 as the key directs. If the shell has plaits or denticles extendir 

 far back into the whorl, the key identifies it as belonging to tl 

 family Strobilopsidae. But as this shell has no plaits, you ne: 

 consult couplet 3. Because the shell is dome shaped, you mo\ 

 to couplet 4, and because it has a lip with a sharp edge you coi 

 suit couplet 7. The coarse ribs of the shell identify the sna 

 as belonging to the family Endodontidae. 



Keys to the genera. — Turning to page 83, you find a ke 

 to the genera of the family Endodontidae. In the first couple 

 you read: "Shell M to 1 inch in diameter and marked by brow 

 spiral bands or scattered blotches of brown color," and "She 

 M inch or less in diameter and without contrasting marking: 

 even brown or horn in color." As your shell is nearly an inch i 

 diameter, you know it belongs in the genus Anguispira. Tun 

 ing to the key for this genus, page 84^ you find: "Whorls wit 

 irregular vertical dashes and spots," and "Body whorl with tw 

 horizontal stripes." As your shell has a body whorl with tw 

 horizontal stripes, you decide that its name must be Anguispit 

 kochi. 



Using the keys. — The keys contained in this fieldbook ar 

 based on the most obvious characteristics of the shells of adu. 

 specimens found in Illinois. They will not aid in the identificj 

 tion of young or immature snails. For instance, shells of th 

 immature specimens of Polygyra have a thin lip with sharp edg< 

 whereas shells of the adult snails of this genus are characterize 

 by a reflected or turned-over lip. Young polygyras are likely t 

 be confused with adult specimens belonging to the famil 

 Endodontidae or even with those of the large Zonitidae. Pol> 

 gyra shells differ from those of the Endodontidae in usuall 

 being yellowish in color and from those of the Zonitidae i 

 having a surface which is never smooth or polished. Youn 

 snails are usually found with adult specimens, and the gener? 



