62 TRANSACTIONS OF THE WAGNER FREE 



Of course, as before noted, the mechanical principles are the same in any 

 group of gastropods, but among those in which the wrinkling is confined to 

 the region of the aperture or those shells which are Urate or dentate as opposed 

 to plicate, several other principles come into play which may be briefly referred 

 to in passing, In the first place, those species which have a very extended 

 mantle, with hardly an exception have a lirate aperture {Oliva, Olivella, Cy- 

 prcea, Trivia, etc.). With species in which there is a widely expanded man- 

 tle and yet no lirations, it will usually be found that the mantle is not entirely 

 withdrawn into the shell in such forms, oris permanently external to the shell 

 (many Opistliobranchs, Marseniidce, Sigaretus, Harpa, etc.). In a group, like 

 the CyprcBidcB, where nearly all the species are lirate on both lips, there are a 

 few which want these lirjE, and these are species which have a wider aperture 

 in the adult than most of the genus, and in which we should expect the wrin- 

 kling would be less emphatic. 



In most turrited gastropods the lirae inside the mouth are not very regular 

 in number or position compared with such forms as the Cyprceidcz. The 

 former are mostly species which have a nearly smooth mantle-edge without 

 any fringe of papillae or tentacular processes upon it and hence its wrinkling 

 will be more or less governed by fortuitous circumstances. But when (as 

 in Cyprcea, many Trochidce, Turbinida, etc.) the edge of the mantle is more or 

 less regularly studded with tactile papillae which are less contractile than the 

 mantle itself, are thicker and regularly spaced, it will be seen at once that their 

 presence will have a marked effect in determining the number and position of 

 the wrinkles and consequently of the lirse, and in this way the singular uni- 

 formity in number and position of the lirae or " teeth " in such forms as Cy- 

 prcea can be accounted for. On the other hand, if we take a form like Ovidiim 

 gibbositm, which has much the shape of Cyprcea, but has no regular lirae, and 

 examine the soft parts, we find that the margin of the mantle is devoid of 

 papillae, the mantle itself is extremely thin, and the aperture of the shell wide 

 enough to receive the whole without any noticeable compression, and hence 

 there is no mechanical reason why lira; should be developed upon its margin. 

 Compare, for instance, on H. & A. Adams' plate xxviii. (Genera of Recent 

 MoUusca, 1858) the beautifully fringed mantle-margin of the half dozen Cy- 

 prsas there figured, with the smooth edge of the same organ in Calpiirmis on 

 the same plate. But, as if to show that the papillse are not essential to the li- 

 ration, though they regulate and guide its formation of the wrinkles which 

 produce it, we see, on the same engraving, that the difference between Ovidum 

 or Calpurnus and Cyprcea is not merely that in the latter both lips of the 

 aperture are lirate and in the former only one, and that often very feebly, but 

 that in the Cyprcea the denticulation is constant and regular, while with the 

 smooth-edged mantle it is inconstant, irregular, feeble or even absent. So it 

 may be considered as demonstrated that the liration is produced by the me- 

 chanical wrinkling, but regulated by the marginal appendages and the amount 



