69 



Altogether tlic fresh water shells of Tasmania present a 

 novel and peculiar character which, when carefully studied, 

 may help to explain much of the distinctive zoology and 

 geology of the island. So far as my observations go, its 

 results seem more adverse than favourable to the Darwinian 

 hypothesis, but the nature of this paper prevents my stating 

 at any length the reasons which incline one to this opinion. 



UNIVALVES. ANCYLUS. Geoffroy, 1767. 



(Traito des coquillcs de Paris par Etienne Louis Geoffroy, 

 Paris, 1767.) 



Tcstn tenuis, oblique conica, apice acuto, posterius inflexo, apertura 

 ovali ; margiuihtis simplicusimis. 



Shell thin, obliquely conical, apex acute, posteriorly in- 

 flated, aperture oval with quite simple margins. 



These freshwater limpets are air breathers, and not nume- 

 rous in species. They are found, says Mons. Bourguignat 

 (who has made the genus the subject of a most elaborate paper 

 in the Zool. Soc. Proceed, for 1853 p. ^7) in all the great 

 divisions of the world, but the section Velletia has hitherto 

 only been found in Europe. About 50 species are known. 



Ancylus cumingianus, Bourguignat (loc. cit.) A. testa antice 

 gibboso-co7ivexa, postice concava, apice recurvo, contorto, ad marginem 

 aperturce lateralem dextrorsus dejecta, ac duos anfractos prcebente ; 

 anfraictibus depnssionem apicalem convexitate penultimi obtegentibus. 

 Testa parum dinphana, 1(evi vel striata, prcesert/im ad aperturam ; 

 anfractibiis apicis scepissimi rugoso-radiatis ; epidermide supra cornea 

 vd virescente, ijiiws albida ; apertura subangulato-rotundatak 



Shell gibbosely convex anteriorly, posteriorly concave, apex 

 recurved, twisted and dextrally turned down to the lateral 

 margin of the aperture, so as to make two whorls ; whorls 

 covering the apicial depression by the convexity of the 

 penultimate. Shell slightly diaphanous, smooth or striate 

 about the aperture, the apicial whorls very often rugosely 

 radiate, epidermis greenish or horny above, white within ; 

 aperture subangulately rounded. Length 6 — 7. Breadth, 

 5 — 5^. Alt., 1\ — 3 mill. But specimens have been placed in 

 my hands by Mr. Legrand of nearly double this measurement. 



This species is truly the finest Ancylus known, having no 

 congeners in any way approaching it. Laiia neritoides of New 

 Zf'aland may be compared with it in some respects. Its peculiar 

 features are its size, the excessive deviation of the apex, its 

 ]»eculiar spiral apex, its mode of growth and the form of 

 its aperture. These separate it completely from all species 

 hitherto known. Habitat, in streams between New Norfolk 

 and Hamilton. The large ones referred to from a small 



