XI THE GALAPAGOS BRAZIL 357 



is uncertain, is peculiar to New Grenada. The land operculates 

 are few in number, and in Bolivia almost disappear. They 

 belong principally to Neocyclotus (of which 11 species occur in 

 Venezuela and Colombia) and Helicina (10 species in the same 

 district), besides the stragglers already mentioned from AVest 

 Indian sources, and a few Gydophorus. Bourcieria is a form of 

 Helicina peculiar to Ecuador. Amjoullaria, with Ceratodes, a 

 peculiar planorbiform sub - genus, and Hemisinus, form the 

 bulk of the fresh-water operculates. 



The Galapagos. — Thirty-four species of land Mollusca, all 

 peculiar, are known from these islands; 25 of these are forms 

 of Bulimulus. There are no Helicidae, one each of Hyalinia, 

 Leptinaria, and Helicina, and two Pupa. The Bulurmlus are 

 mostly of the group Nesiotis, and in their brown colour bear 

 some outward resemblance to the dark Achatinella of the Sand- 

 wich Is., living as they do mostly under scoriae on the ground, 

 and not on trees. In type, however, tl:ey appear to be derived 

 from Chili and Peru, rather than from the parts of S. America 

 immediately contiguous. Another section {Pleuropyrgus 2 sp.) 

 closely resembles a marine Chemnitzia. The islands are all 

 volcanic, and are probably not the result of subsidence ; thus the 

 existing species are not to be regarded as the relics of a more 

 widespread fauna, but as a new set of inhabitants. 



(4) The Brazilian Sub-region. — This immense district is very 

 little known, except in the south, and it is consequently im- 

 possible to give any satisfactory account of its Mollusca. It is 

 possible that eventually it will be found tliat it falls into 

 provinces which correspond more or less to (a) the Amazon basin ; 

 (&) the mountainous district in the east, drained by the Tocantins 

 and the San Francisco ; (c) the Parana basin in the south central 

 district ; and (d) the Argentine or Pampas district in the extreme 

 south. But at present the data are insufiicient to establish any 

 such subdivisions, whose existence, if proved, would have an 

 important bearing on the problem of the coalescence of S. 

 America into its present form.^ 



The Agnatha are represented by Streptaxis alone (17 sp.). Helix 

 is rare, but includes the peculiar Polygyratia (Fig. 150, A, p. 246), 

 while Lahyrinthus (2 sp.), Solaropsis (5 sp.), and Systrophia are 



' Comiiarevon Martens, Malak. Bldtt. 1868, p. 169 ; von Ihering, Nachr. Dcutsch. 

 Malak. Gcsell. 1891, p. 93. 



