PEEUYIAlNr JiEGION. 113 



others dry, rocky and rainless, especially in the south; it is 

 watered by numerous streams — the affluents of the Amazon and 

 Plata. The hydrogranhical areas of these two great rivers have 

 been represented on the map, but the southern boundary of the 

 Brazilian Province extends beyond the line of watershed to 

 the tropic, including the head- waters of the Plata, in which the 

 same remarkable fresh-water bivalves are found as in the 

 Bolivian streams. (D'Orbigny). The mountains around the 

 Lake Titicaca are the highest in the New World, and there 

 M. D'Orbigny found several species of Helix up to the elevation 

 of 14,000 feet; Bulimus Tujpaici ranges to 9,000 feet. The large 

 and typical species of Bulimus belong to this province ; B. ovatics 

 and oblongus are found near the coast (p. 291), and B. maximus 

 farther inland. The auriculoid Bulimi {Otostomus, and Pachy- 

 otis, Beck), those with an angular mouth {Goniostomus, Beck), 

 and the pupiform species, with a toothed aperture, (^Odonto- 

 stomus), are characteristic of this region, and also some of the 

 most elongated forms {Oheliscus). The lamp snails {Anastoma) 

 and Megaspira, genera inhabiting France during the Eocene 

 period, are now peculiar to Brazil ; Simpulopsis is also peculiar, 

 and Streptaxis attains its maximum there. The Cydostomidce are 

 few, and the other West Indian forms have almost disappeared. 



Helix...... 47 Glandina 1 Cyclophorus , 2 



Streptaxis •••• H Tornatellina 1 Cyclotus 1 



Anastoma 7 Vitiina 5 Cistula ,.,, 1 



Bulimus 250 Omalonyx....... 1 Helicina 12 



Megaspira 2 Simpulopsis 5 



The land slugs are Peltella paUiolum, Vaginulus solea, and 

 1 Limax andicolus. The fresh- waters of the interior are rich in 

 bivalves of peculiar genera :* — 



Physa.,.. 1 Ampullaria 2 Unio 4 



Ancylus 1 Corbicula 2 Iridina 1 



Planorbis 4 Pisidium 1 Hyria 1 



Paludestrina 2 Anodon 1 Castalia 2 



Marisa 1 MonocondylEea., ........ 1 Mycetopus 3 



Succinea 27 



24. PERTJYiAisr Eegion. 



The long an4 narrow tract between the Andes and Pacific, 

 extending from the equator to 25° S. lat. forms a distinct, 

 though comparatively unproductive province, including the coast 

 of Ecuador, Peru, and Bolivia. It is warm and almost rainless ; 



* The American Expedition explored forty Brazilian streams, and found only one 

 jAmpullaria, one Melania^ and one Planorbis. ((Joi^d.) 



