Appendix to Part I. 175 



semilunaris superne extm angulatd, labio externa tenui: interna 

 plicis duabus spiralibus, posticd majori: lang. 0*15, lot. 0"83. 

 poll. 



The young shells of this species have very different proportions 

 from those marked above, their axis being nearly as great as their 

 "width. The largest specimen is white, with irregular ferruginous 

 rays. This is very different from any known recent species, although 

 there are several to which it appears to have some analogy, such as 

 Helix epistylium or Cookiana, and H gularis : in both of these, 

 however, the internal spiral plaits are placed within the outer wall 

 of the shell, and not upon the inner lamina, as in Helix bilamellata. 

 There is another recent species, which is somewhat analogous to 

 this ; it is as yet undescribed, and differs from this and from 

 Cookiana, in the circumstance of its possessing four internal spiral 

 plaits, two of which are placed within the outer, and two upon 

 the inner wall of the shell ; it was brought from Tahiti, in the 

 Beagle. 



2. Helix polyolo:n\ G. Soiverby. 



Testa orhiculato-subdepressd, anfractibus sex, rotundatis, striatis ; 

 aperturd S' milunari, labio interna plicis tribus spiralibus, posticis 

 gradatim majoribus, externo ivtus dentibus quinque instructa ; 

 umbilico mediocri : long. 0"07, lai. Q'\b,p>ott. 



This is somewhat related to Helix contorta of De Ferussac, 

 'Moll. terr. et fluv.' Tab. 51 A, f. 2 ; but differs from it in several 

 particulars. 



3. Helix sptjeca. G. Sowerby. 



Testa suborbiculari, spird subconoided, ohtusd ; anfractibus quatuor 

 tumidis, substriatis; aperturd magna, peritremate tenui; umbilico 

 parvo, pro] -undo : long. OT, lot. 6-18, poll. 



Easily distinguished from Helix polyodon, by its wide, toothless 

 aperture. 



4. Helix biplicata. G. Sowerby. 



Testa orbiculato-depressd, anfractibus quinque rotundatis, striatis ; 

 aperturd semilunari, labio interna plicis duabus spiralibus, posticd 

 majori; umbilico magno : long. O04, lat. OT, poll. 



This must be regarded as perfectly distinct from Helix bilamellata. 

 on account of its form ; its umbilicus is much larger, its spire is not 

 flat, nor is the posterior edge of each volution angular. There are 

 specimens, which must be referred to this species, found with the 

 foregoing species, and with the Cochlogena fossilis, which latter is 

 associated with a living Succinea, in the modern calcareous sand- 

 stone. 



