Mr. W. H. Benson on new species of Helix. 255 



apice obtuso, rubente ; anfractibus 4 convexis ; apertura elliptico- 

 ovata, spiram superante, plicis duabus coarctata ; plica I lamelli- 

 formi parietali, intrante, hyalina, 2iida columellari dentiformi, ad 

 angulum columellse truncatae posita ; columella lata, verticali, hy- 

 alina, oblique lateque triincata, margine dextro simplici, acuto. 



Long. 3 mill., diam, 2-2^ mill. 



Hab. in sepibus apud Moka Insulse Mauritii. 



I discovered this ioleresting little species in February 1847 

 in the grounds of Sir D. Barclay at Moka, creeping in showery 

 weather on the leaves of Niccioli hedges. The animal was Heh- 

 eiform, and I noted it at first in my journal as an Achatina, with 

 reference to the truncation of the columella, until the retraction 

 of the animal admitted a view of the parietal plica which winds 

 into the interior of the shell. In form this species much resem- 

 bles Tom. globosa, Petit, but differs in its thinness, sculpture 

 (when viewed under the lens), and in the plaits of the aperture, 

 &c. In iis short, twisted, abruptly truncated columella, and in 

 the winding' callous ridge on the parietes, the Bolivian Achatina 

 concentrica, Reeve, ' Conch. Icon.^ pi. 19. f. 106, is related to 

 T. Ce/nica, and will perhaps form another species of the genus. 

 T. Cemica affords the only example of this genus known to in- 

 habit the isles of the Indian Ocean ; the s])ecies recorded by 

 PfeifFer, Petit, and others being confined to the Pacific Ocean, 

 the West Indies and South America. I took only two specimens, 

 bi^tSir D. Barclay writes that he has since been more successful 

 in its capture. I have named the species from " Cerne,'"' one of 

 the appellations of the beautiful island which produces it, and 

 which, with reference to its extent, is so prolific in the land mol- 

 lusca. 



It is further worthy of note that Helix unidentata and H. Ce- 

 poides, gigantic in their genus, seem to indicate a transition from 

 this form, through H. Studeriana, to the more regular forms of 

 Helix ; and that among these, H. unidentata and H. Siudeiiana 

 inhabit the neighbouring island group of the Seychelles. 



The Succinea which accompanied Helix paludicola at the Cape, 

 and which may be S. Chiloeasis, Pfr. {S. elongata var. 7, Per.) is 

 decidedly amphibious, notwithstanding the o{)inion of some 

 authors. Dropped into water, it, at first, crept out of it, but pre- 

 sently I observed it descending, of its own accord, below the 

 margin of the liquid, and twice, within the space of a few mi- 

 nutes, I saw it take to the water, and swim resupinate at the 

 surface like a Lajmncea, and ascend the opposite side of the glass 

 vessel in which I had placed it. I was particular in the exami- 

 nation of the animal, with reference to this singular action, and 

 found the upper tentacula short and thick, with the eyes or per- 

 cipient points at their apex, the lower pair being very short ; the 



