CHAP. VI. THE LTJCERNINiE. I9I 



of which, in doubtful cases, will almost always he a 

 sufficient guide: — 1 . The very marked depression of their 

 whole form, and the great number of the spiral whorls. 

 2. The possession of teeth either on one or on both sides 

 of the aperture : and, 3. The granulated, or distinctly 

 striated, surface of the shell. As our analysis has not 

 been carried down to the location of all the sub-genera, 

 we shall merely, in this place, enumerate the primary 

 groups or genera, with some few of the sub-genera, leaving 

 the rest for the more systematic department of the vo- 

 lume. 



(176.) The groups which appear to rank as genera, 

 and which are therefore the first divisions, are the fol- 

 lowing : — 1 . Lucerna, having the shell flattened and 

 orbicular, the margin always carinated, and generally 

 sharp ; the whorls numerous ; the surface granulated, 

 but never striated ; and the aperture usually toothed, but 

 the teeth confined to the inner lip.* 2. Lucernella, 

 equally depressed with the preceding, but the margin of 

 the body- whorl is rounded and convex ; the outer lip 

 is always toothed, and there are opposite teeth on the 

 inner lip. These appear the two typical divisions. The 

 three aberrant are, the broad-lipped species of Ferussac's 

 sub-genus Helicella, having the body-whorl unusually 

 large in proportion to those of the spire, which is flat- 

 tened ; the umbilicus deep ; the outer lip spreading, 

 and diffuse, but rarely provided with any toothlike pro- 

 jection : these form our genus Hemiodon. The next, 

 or most aberrant type, is composed of a part of Ferus- 

 sac's Helicogena, where the shell is granulated, the spire 

 depressed, and the outer lip marked at its base with 

 toothlike notches ; the spire is very small, and hardly 

 makes three volutions : this is our genus Thelidomus. 

 The wide aperture of these prepare us for Leiostoma, 

 having the aperture remarkably large and particularly 

 smooth and glossy, while the glazing of the inner lip is 

 extended very much beyond its usual circumference, 



* Except in Anastoma, which represents Pupa and Clausilia. 



