22 ILLINOIS NATURAL HISTORY SURVEY MANUAL 



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

 which a species may be identified by certain characteristics or 

 combinations of characteristics that are pecuHar to it. 



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

 snail with brown rolor bands encircling its coarselv ribbed, dome-' 

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

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

 into which it can withdraw," and "Animal having onlv a rudi- 

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

 and well-developed; so you consult both parts of couplet 2, 

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

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

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

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

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

 sult couplet 7. The coarse ribs of the shell identify the snail 

 as belonging to the family Endodontidae. 



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

 to the genera of the family Endodontidae. In the first couplet, 

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

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

 M inch or less in diameter and without contrasting markings; 

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

 diameter, you know it belongs in the genus Anguispira. Turn- 

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

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

 horizontal stripes." x^s your shell has a body whorl with two 

 horizontal stripes, you decide that its name must be Anguispira 

 kochi. 



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

 based on the most obvious characteristics ot the shells ot adult 

 specimens found in Illinois. They will not aid in the identifica- 

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

 immature specimens oi Po/ygyra have a thin lip with sharp edge, 

 whereas shells of the adult snails ot this genus are characterized 

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

 be confused with adult specimens belonging to the family 

 Endodontidae or even with those of the large Zonitidae. Poly- 

 gyra shells differ from those of the Endodontidae in usually 

 being yellowish in color and from those ot the Zonitidae in 

 having a surface which is never smooth or polished. 1 oung 

 snails are usually found with adult specimens, and the general 



