190 SHELLS AND SHELL-FISH. PART I. 



derstood the difference between analogy and affinity'^, 

 so lamentably confounded by so many other naturalists, 

 even of the greatest reputation. The analogy, again, 

 which the large coriaceous mantle, or shield, of Onchi- 

 dium has to the Chitons need hardly be adverted to. 

 The three aberrant genera, Vitrina Drap., Stenopus 

 Guild., and Succinea Drap., have turbinate shells, nearly 

 or quite sufficient to include their bodies ; but these 

 coverings are generally thin and semi-transparent, with 

 a wide aperture, a very short or small spire, and, ge- 

 nerally, with only the vestige of a pillar. For the dis- 

 covery of the singular animal of Stenopus cruentatus t 

 (fig. 33.), science is likewise indebted to the lamented 



Guilding: it seems intermediate between Vitrina and 

 Succinea, and will thus stand as the most aberrant of 

 the whole. The connection of this sub-family to the 

 freshwater snails is obviously effected by Succinea; 

 while Vitrina leads immediately to Leiostoma, among the 

 land volutes. The sub-genera not having yet been 

 determined, we shall pass at once to the fifth division, 

 which closes the circle of the HelicidtB. 



(175.) The terrestrial volutes, or lamp-snails, Lucer- 

 NiN^, were named by Humphreys, — a name we retain 

 for the whole group, which, as we have already seen, 

 constitute a sub-family.;}: They are well distinguished 

 from the typical HelicirKS by three characters, any two 



* " Genus PlanarUs facie quam plurimum analogttm, ut Limacides re- 

 spirationis modo, locis, moribusque omnino nffine." — Guilding MSS. 



t See figures and description in Zool. Journal, iii. pi. i5. figs. 1—5. 



X Lamarck subsequently used the name Caracolla, which Ferussac 

 wished to set aside for that of Helicudonta, a name which, even had it the 

 priority, implies two errors ;— first, that they belong to the typical Helices; 

 and secondly, that they all have teeth : we consequently cannot adopt the 

 innovation. 



