CHAP. VI. ANALOGIES OF PUPA. 16Q 



Analogies of the Genera Pupa and Clausilia. 



Sub-geiiera Sub-genera Genera 



of Analogical Characters. of of the 



PcpA. Clausilia. Helicin^. 



r Sub-typical ; whorls nume-^ 

 Megaspira. ^ rous, all persistent ; umbi- V^a/ca. Helix. 



C licated. 3 



f Typical ; spire deciduous ;T 

 Siphonostoma. < lips generally detached from > Clausilia. Geotrochus. 



C the body-whorl. j 



r Outer lip with the margin, T 

 Plicadomus. < considerably dilated, and > Macrodontes. Pupa. 



C the edge reflected. J 



Pupa. [^"who/ir'' ""'^^ ""'"^'■°"']PMp^«a. ? 



Gonospira. pj^reof^few whorls, and very j p Helicella. 



The resemblances between the sub-genera of Pupa 

 and those of Clausilia are too obvious to be dwelt 

 upon ; but those between the first column and the last 

 require some explanation. The spire of Helix is al- 

 ways obtuse, so is that of Megaspira ; in Geotrochus 

 and Siplionostoma, on the contrary, the terminal por- 

 tion of the whorls is acutely conic ; and this form is 

 carried to such an extent in the deciduous portion of 

 some species, that they actually put on the appearance 

 of being long-spired trochiform shells, instead of a 

 portion only of that to which they really belong. He- 

 licella and Gonospira agree in the paucity of their 

 whorls; while the fifth type, which should represent 

 Pupa, has not been determined. If we wished to carry 

 our analogies into the zoophagous tribes, it is clear that 

 the strombiform type is the third, and the volutiform 

 the fifth, of the above series. 



(158.) We feel unprepared to offer any definite opi- 

 nion on the extent or the subordinate types of the genus 

 Helicella ; it stands at the confines of the HELiciNiE and 

 the Luc?:hnin^, and therefore may be supposed to par- 

 take in the characters of both. AVe even think that 

 several of the perfectly discoid shells, now arranged 

 with Cyclostoma, such as Cy. planorbula*, will event- 



* Ency. Meth.4ol. fig. 3. 



