XI THE GALAPAGOS — BRAZIL 357 



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

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

 They belong principally to Neocijclotus (of which 11 species 

 occur in Venezuela and Colombia) and Heliciyia (10 species in 

 the same district), besides the stragglers already mentioned from 

 West Indian sources, and a few Cydoplicrus. Bourcieria is a 

 form of Helleina peculiar to Ecuador. Ampullar ia^ with Cera- 

 todes, a peculiar planorbiform sub-genus, and Hemisinus^ form 

 the bulk of the fresh-water operculates. 



The G-alapagos. — 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 Bulhnulus 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, they appear to be derived 

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

 immediately contiguous. Another section (^Pleuropyrgiis 2 sp.) 

 closely resembles a marine Cheninitzia. 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 

 impossible to give any satisfactory account of its Mollusca. It 

 is possible that eventually it will be found that 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 (t7) the Argentine or Pampas district 

 in the extreme south. But at present the data are insufficient 

 to establish any such subdivisions, whose existence, if proved, 

 would have an important bearing on the problem of the coales- 

 cence 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 Systro- 



1 Compare von Martens, Malak. Bldtt. 1868, p. 169 ; von Ihering, Nachr, 

 Deutsch. Malak. Gesell. 1891, p. 93. 



