24 THE NAUTILUS. 



genera in their late development, if they do not maintain it to matur- 

 ity, possess a coiled shell and upon this the limpet-like shell of 

 Ancylus is secondarily developed. It may be further noticed that 

 these latter genera are all sinstral and I am under the impression 

 that the anatomy corresponds closely. At any event it is quite dif- 

 ferent from that of Lanx, Laevapex (Ferrissia) and Gundlachia, 

 which do not show any evidence in their post-embryological develop- 

 ment that they ever possessed a coiled shell though I suspect they 

 did at one time far back in their history. I have been hoping to 

 study the early development of one of these genera but it is a little 

 out of my line at present. The latter genera should, I think, at 

 least be segregated in another family, the Laevapecidae, with sub- 

 families Laevapecincz and LancincB, and probably another subfamily 

 for the secondarily coiled forms that may belong here. In this case 

 my statement regarding the simple patelliform ancestors would refer 

 to this family since it was the development of these and not that of 

 the Old World group that I studied. 



In regard to the generic classification of the Laevapecidas there is 

 opportunity for considerable disagreement of opinion. I ' have called 

 attention to the fact that in Lanx, Fisherola and Zalophancylus the 

 sculpture is solely concentric and the apex lies along the medial line, 

 the genera being distinguished chiefly by the position of the apex, 

 which may be central, sub-central, or terminal, arbitrary characters 

 perhaps, but ones which run through a number of species that seem 

 to group together in other respects. In Gundlachia, Kincaiditta* 

 Laevapex, and Ferrissia the problem is much more difficult. I am 

 not by any means sure that I can always tell a non-septate Gund- 

 lachia or Kincaidilla from a Ferrissia. Our local species look easy; 

 but after comparing Walker's figures of African Ferrissias I would 

 not hesitate to call most of the latter non-septate Gundlachias, 

 though I believe Walker knows Ferrissias better than I do. 



I am sorry that Walker has not examined the post-embryonic 

 stages of some large Ferrissia that actually shows the development 

 from Laevapex. Both Ferrissia and Lanx show unmistakable indi- 

 cations of derivation from a very low-spired form such as is repre- 

 sented by Laevapex and Walkerola respectively, as I have observed 

 in at least two species in the former genus and three in the latter. 

 This form I should regard as the least specialized modern type 

 among the Laevapecidse HAROLD HANNIBAL. 



!Proc. Mai. Soc. Lond. x, 1912, p. 147 ff. 



