192 SHELLS AND SHELL-FISH. PART I. 



This latter character is highly important, as showing the 

 analogy of Leiostoma to the LimnacincB, and its affinity 

 to the half-testaceous slugs, or the Limacince. 



(177.) Looking to the above genera, with reference 

 to their analogy, they appear to represent the following 

 divisions in their own family, and in the tribe of the 

 Zoophaga : — 



Analogies of the Lucernin^, or Land Volutes. 



Genera of the 4 , ■ , r^i. , Sub-families of the 



Lucernin^. Analogical Characters. Helicid^. 



LucERNA. [^'^um'"e?ous°' ^''' '''"'' ' ^'^'''^'} Achatin^. 



Hemiodon. Shell discoid ; the spire depressed. Lucernin^. 



Thelidomus. Spire of very few whorls. Limacin^. 



Leiostoma. [ ^P^Sngf ^ '^"'' ' '""" ^'^] L>^'^^"^^- 



(178.) The typical genus Lucerna has one peculiar 

 character, — that although its outer lip is in general 

 toothed or plaited, these plaits are never seen upon the 

 inner lip, or that part of the body-whorl which forms 

 the opposite side of the aperture. They are the largest 

 shells of this sub-fam.ily, and are particularly abundant 

 in the West India islands. Although decidedly de- 

 pressed shells, their spiral whorls are numerous, and are 

 very progressively graduated. We separate them into 

 the five following sub-genera: — In Discodoma,t\ie cir- 

 cumference is carinated, the aperture angular, and without 

 teeth ; and the edge of the outer lip but slightly, if at all, 

 reflected. In Lucerna, the teeth on the edge, or within 

 the outer lip, are very evident. In Anastoma, they are 

 extended all round the aperture, which is likewise 

 turned, so as to be nearly on the same plane as the spire. 

 Leaving these, we have an analogous form to Thelidomus 

 in several small toothless Helices L. (our Lucidella), but 

 which evidently, by their spire, belong to this group. 

 Caracotla completes the circle by uniting to Discodoma, 



