MANUAL OF CONCHOLOGY. 



FAMILY HELIGIDM. 



Shell spiral, elongated, bulimiform, turbinifo*m, trochiform, 

 depressed, lenticular, or planorbiform, usually thicker than in 

 the Zonitidae, and also less transparent than in that family ; the 

 aperture either edentulous or armed with teeth, the lip usually 

 reflected. 



Animal capable of complete retraction within the shell, the 

 tail without mucous gland or projection ; mouth always pro- 

 vided with a jaw, which is striate, ribbed, sulcate or plicate, 

 sometimes composed of several imbricating pieces; radula com- 

 posed of many transverse horizontal series of teeth, the centrals 

 tricuspidate, about the size of the laterals, laterals bicuspid, or 

 tricuspid with the interior cusp obsolete, marginals usually 

 wider than high, shortVwHh two or three small cusps (Struct, 

 and Syst. Conch., i, t. 13, f. 59). 



As to the shell of the heliciform groups it is usually readily 

 distinguished from Zonitidse by the reflected lip of the aperture, 

 which is a character distinguishing most of the larger and most 

 important sections or groups, but this difference disappears in 

 the Patulae, for example, in which the lip is simple and the shell 

 thinner; however, the Patulse are commonly darker in color, 

 often with characteristic chestnut markings, and more rugosely 

 sculptured surface than most Zonitidae. 



In the soft parts the most obvious distinction is the want of 

 a caudal mucous pore in the Helices, and their possessing a 

 sculptured jaw. Typically, there is a distinction in the denti- 

 tion, although in some species the lateral teeth of Helices take 

 on a pseud ozonitoid appearance ; even in such cases the extreme 

 marginals in Helix remajn short and very obtuse. 



The family thus outlined comprises several thousand species, 

 most of the land-snails, in fact ; including not only the numerous 

 groups of Helix proper, but those of Bulimus, Partula, etc., as 

 well. As the consideration of the species will occupy the pages 



(3) 



