Notes on South African Mollusca. 159 



increase in length of the latter organ. Perhaps T. lucautis might 

 l)e regarded as one of the least primitive members of the genus. 



TBIGONEPHRUS AMBIGUOSUS (Ferussac). 

 (PI. II, f. 11). 



1821 Helix (Helicella) ambiyuosa, Fer., Tahl. Syst. Moll. pt. 3. 



p. 47. L. 

 18-18 Helix lucaiia, Miill., var. /3, pcristomatc aurant/cico, Pfr., Mon. 



Hel. viv. i. p. 332. 

 1850 Helix lucana, Miill. (nin/iii//iosa, Fer.), Desh., Hist. Nat. Moll. 



pi. X B, f. 3-5. F. 

 1910 Dorcasia ponsonbyi, Fulton, A.M.N.H. vi. p. 212. D. 



Shell rather large, depressed-glohose, umbilicate, of moderate 

 thickness, translucent, bright corneous above, much paler, shading 

 to grey, beneath ; peristome and callus bright orange-brown. 

 Spire but little raised, apex sub-mamillate, bluntly rounded. 

 Whorls 4^, rounded, rapidly increasing, the first 1A- smooth, re- 

 mainder covered with close, faint, curved striae, becoming rather 

 fainter beneath, with little malleation, but with tracts of micro- 

 scopic granular sculpture, which is most apparent on the upper 

 portion of the last whorl. Suture simple, shallow. Aperture 

 truncate-ovate ; peristome narrowly reflexed and a little thickened, 

 ends joined by a thin callus. Umbilicus deep, but narrow and a 

 little strangulate. 



Dimensions of a cotype of ponsonbyi from Mossel Bay, in my 

 collection : Diam. maj. 28 - 3, min. 23'1 ; alt. max. 15 - 8 ; apert. 

 15'7 x 11'7 mm. ; ends of peristome 7'7 mm. apart. 



Animal unknown. 



Hab. CAPE OF GOOD HOPE. Le pays des Hottentots (Ferussac) ; 

 Mossel Bay (Gibbons) ; Vleesch Bay (Power). 



Type of ambiguosa, ubi? that of ponsonbyi in British Museum. 



Ferussac first published the name ambiguosa among a number 

 of other uncharacterized species, but gave an acceptable locality. 

 Deshayes' conception of the species as lucanus is erroneous, but 

 as he expressly states, in the explanation of his plate, that the 

 shell thereon figured as lucanus is ambiguosa, Fer., the latter name 

 is clearly established. The figure in question is a very good one of 

 Dorcasia ponsonbyi, Fulton, and this name must, therefore, be 

 relegated to synonomy. 



The comparative breadth of the last whorl varies greatly in 

 this species. In most examples it expands considerably towards 



