COLIMACEA. MOLLUSCA- HELIX. 183 



Shell small, orbicular, slightly elevated, the apex a little de- 

 pressed, concave beneath, brownish horn-colored, smooth, thin, 

 fragile, pellucid, shining ; whorls fine, slightly rounded above, 

 separated by a well-impressed suture, marked with very fine lines 

 of growth, more decidedly wrinkled at the suture ; beneath very 

 smooth, regularly rounding into a moderately large, deep, and 

 well-developed umbilicus ; aperture rounded ; lip simple and thin. 

 Diameter commonly one fifth of an inch, sometimes one fourth. 



Animal has the head and tentacula blackish, upper parts bluish, 

 posterior parts whitish, transparent. Foot thin and narrow. 



'A very common species, always to be found about decaying 

 stumps, old logs, &c. It has been noticed in nearly every part 

 of the continent. 



This shell has very little to distinguish it except its very simple 

 structure. It is like H. celldria except in its smaller size. Helix in- 

 dentdta and guldris have both a similar size and external appearance ; 

 but the first is known by its distant, impressed, radiating lines, and the 

 second by the peculiar tooth within its aperture. Ferussac supposed 

 it to be a variety of H. lucida, Drap. ; but our shell has the umbilical 

 region more excavated, and the umbilicus larger ; there is also one 

 whorl less, in shells of the same size, so that the surface appears less 

 crowded. The aspect of the two shells, on comparison, is sufficiently 

 diverse. H. electrina has also one whorl less, and has a much more 

 polished appearance. 



Occasionally, a thickening of the shell seems to take place at inter- 

 vals, so as to produce an opaque appearance. 



HELIX ELECTRINA. 



Shell small, depressed, pellucid, fragile, amber-colored ; whorls 

 four, conspicuously wrinkled by the lines of growth ; aperture 

 rounded ; lip simple ; umbtlicated. 



FIGURE 111. 



State Coll., No. 107. Soc. Cab., No. 2392. 



In the size, depressed-conical shape of the upper surface, the 

 number of whorls, and the rapid enlargement of the lowest whorl, 

 this shell corresponds with H. indentata. It differs in its darker, 



