COLOMBIA AND VENEZUELA 



355 



been usual to separate off the two latter countries as forming a dis- 

 tinct " Peruvian " sub-region ; but there is, as will be seen, abso- 

 lutely no line to be drawn between the Mollusc a of Peru and those 

 of Ecuador ; nor would one, on geographical considerations, expect 

 to be able to draw such a line. A better method of subdivision, 

 so far as the species of the whole eastern portion of the region 

 are concerned, would be to group the Mollusca according to the 

 altitude at which they occur, were it not that the evidence on 

 this point is at present but fragmentary. We know, however, 

 that all along the line of the Andes certain species, more parti- 

 cularly of Bulimuhcs, occupy their own zones of elevation, some 

 ascending as high as 10,000 feet above the sea, and never occur- 

 ring on the plains. 



In the northern portions of this sub-region. Central American 

 and West Indian influence is felt to a certain extent. Thus there 



Fig. 233. — A, Orthalicus 

 Deburghiae Reeve, 

 Ecuador ; B, Bulimus 

 (Pachyotus) egregius 

 Jay, BraziL 



are eight G-landina and one Streptostyla in Venezuela and Colom- 

 bia together with one or two species of Cistula, Chondropoma, 

 Proserpina, and Cylindrella, while a single Strophia (decidedly 

 a straggler) occurs at CuraQao. In Demerara and Cayenne there 

 are three or four species of Dente.llaria, In Ecuador, however, 

 Grlandina diminishes to three species, and in Peru disappears 

 altogether, although one Streptostyla occurs. Similarly the 

 West Indian operculates are reduced to one Chondropoma 

 (Ecuador) and disappear entirely in Peru. 



