2,^2 PANAMIC, PERUVIAN, AND MAGELLANIC SUB-REGIONS chap. 



pairs of species, which, while specifically distant, are evidently 

 closely related to one another. Amongst these are, on the 

 Panamic side. Purpura speciosa, Gypraea cervinetta, Cassis ab- 

 hreviata, Natica Chemnitzii, and Stromhus gracilior, correspond- 

 ing to Purpura deltoidea, Cypraea exanthema, Cassis inflata, 

 Natica maroccana, and Stromhus pugilis, on the Caribbean. It is 

 reasonable to conclude that these " analogous species " are 

 descendants of a stock which was common to both seas when the 

 isthmus was open (probably not later than Miocene times), and 

 which have, since the closino; of the isthmus, become modified, 

 some species considerably more than others. 



Among the characteristic genera (compare p. 3) are Conns, 

 Pleurotoma, Terebra, Murex, Purpura, Oliva, Northia, Cantharus, 

 Columbella, Anachis, Cypraea, Stromhus, Cerithium, Coecum, 

 Crepidula, Crucihulum, Vitrinella ; Tellina, Semele, Tellidora ; 

 and Area. 



(4) The Peruvian Suh-region extends from Payta in Peru to 

 about the latitude of Conception in S. Chili (37° S.), being 

 checked from further extension southward by the cold Humboldt 

 current, whose force is distinctly felt as far north as Callao. This 

 cold current thus produces the same results as the similar current 

 which impinges on S. Africa, but has even more effect in decisively 

 separating the fauna on the two sides of the great peninsula, 

 scarcely a single species being common to the western and eastern 

 coasts of S. America. The characteristics of the coast-lines them- 

 selves contribute to this result. The Chilian coast is rocky, and 

 descends abruptly to a great depth, while that of Patagonia and 

 Argentina is sandy and very shallow to a great distance from 

 land. 



The characteristic genera are Cancellaria, Columbella, 3Ionoeeros, 

 Concholepas, Trochita, Fissurella, Chiton; Ceronia, Malletia, and 

 Cumingia. Some of the Californian genera, absent or poorly 

 represented in the Panamic Sub-region, reappear in Chili, e.g. 

 Scurria, Tectitra, and Chlorostoma. 



(5) The Magellanic Suh-region includes the coast -line and 

 adjacent islands (with the Falklands) from Conception in 

 S. Chili to about Port Melo in Eastern Patagonia (lat. 45° S.). 



The principal genera (many of which find a habitat on the 

 gigantic Macrocystis which grows on every rock at low water) are 

 Euthria, Voluta (6 species, one, V. magellanica, the largest known). 



