46 Helix Tatesii. [zoe 



these ci'evices between the shelving ledges, and finding them moist 

 and cool, would continue their explorations until they entered the 

 chambers of the cave; and thus having easy ingress and egress, they 

 have no doubt continued their visits for many years, on the approach 

 of the dry season, while some, perhaps, never leave the cave. 



The fact that there are so few specimens found within the cave, 

 and so many outside and miles away, aestivating under stones, is 

 sufficient evidence that the presence of this mollusk within the cave 

 is simply accidental, and that it is not its natural habitat. 



In his remarks upon this shell. Dr. Cooper calls attention to its 

 resemblance to Planorbis and Ammonite, its relations to H.f poly- 

 gyrella and Gastrodonta, and its afifinity to Macrocyclis, with all of 

 which I agree, and which goes to show very plainly, I think, that 

 nature does not represent any particular genus by the shell. If she 

 indulges in such freaks as genera at all, she determines that matter 

 by modifications of the structure of the animal, and not by the 

 object formed or moulded by the animal itself; and this little shell, 

 compounded of several so-called genera as it seems to be, is a good 

 illustration of this fact. 



In support of this I can do no better than repeat Dr. Cooper's 

 own words: " It w^ould have been supposed to be a Planorbis if 

 found near water and if the streams in that country had not been 

 thoroughly searched by many collectors. It resembles Planorbis 

 in the inverted spire and in the partial enclosure of each whorl in 

 the next larger, so that the spire shows only a small portion of the 

 whole shell. 



"The consequent vertical narrowing of the aperture, and, in- 

 deed, of the whole interior, is also found in some species of Plan- 

 orbis, but not in any American Helicoid. Indeed, it is inconsistent 

 with the character 6f ' Helix,' as defined by Lamarck, and this 

 shell could not, therefore, be embraced in that most comprehensive 

 genus. The resemblance to an Ammonite is conspicuous in a lat- 

 eral view. It probably belongs to Helicellidae, notwithstanding its 

 thickened labrum, which we find also in H. ? polygyrella and G. 

 interna, and some other species. Though toothless, it is apparently 

 nearly allied to the former, in which the spire is fiat and of 7 to 8 

 whorls. It also shows affinity to Macrocyclis in the oblique flat- 

 tening of the outer whorls and its strong deflection near the 

 mouth." 



