CHAP. VL SUB-GENERA OF PUPA. iGj 



at once proceed to the genus Pupa, the passage to which 

 has been opened by Geomitra. 



(157.) The genus Pupa we shall restrict to those 

 maggot-shaped cylindrical shells whose body- whorl is 

 larger than the others, whose spire is thickened in the 

 middle, and which have no teeth on the inner lip ; the 

 aperture also, in three out of the five sub-genera, is 

 always round, but in the two others it is oval, on account 

 of their blending into the genus Clausilia. Having 

 analysed both these remarkable genera, we feel much 

 more confidence in stating the types than in what has 

 been said regarding those of Helijc and Geotrochus. The 

 type of this present group is that extraordinary and 

 rare shell the Megaspira of Lea, of which a noble spe- 

 cimen, containing no less than twenty-two whorls, is in 

 our cabinet. The outer lip is thin, and the inner want- 

 ing ; but there are four sharp plates close together at 

 the base of the pillar, and a central one on the inner side 

 of the body- whorl : it must be remarked that this shell, 

 although of such excessive length, does not lose the 

 apex of its spire, which is obtuse almost to its very tip : 

 this is an important character, because it is carried on 

 to our sub-genus Gonospira, where this part is the 

 same, but even more obtuse : the volutions, however, 

 are only seven, yet the shell has the same form as the 

 last, so that the spiral whorls are nearly of equal thick- 

 ness ; the aperture is more that of Pupa, being oval ; it 

 is thickened all round, and there is a tooth at the upper 

 angles. This leads at once to the sub-genus of Pupa 

 proper, distinguished from both the foregoing by the 

 suddenly-pointed shape of the apex, and the increased 

 thickness of the two lips, which, as in Gonospira, are 

 united : all the typical species in like manner have a 

 tooth ; but this disappears in such species as pass into 

 Plicadomus, where the inner lip is entirely wanting, the 

 aperture having a dilated margin, and perfectly entire, 

 while the apex of the spire, no longer suddenly con- 

 tracted, is obtuse : it is by this sub-genus, as we think, 

 that the whole group is united to Geomitra ; and it may 

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