CHAP, xiv.] THE NEOTROPICAL REGION. 55 



enumerated ; and 17 of these are found in streams flowing into 

 both the Atlantic and Pacific Oceans. On the whole, ll'tamilies 

 are represented among the fresh-water fish, and about 38 genera. 

 Of these, 14 are specially Nearctic, Amiurus f (Silmid&) ; Fundu- 

 lus (Cyprinodontidae) ; Sclerognathus (Cyprinida3) ; and Lepidosteus 

 (Ganoidei). A much larger number are Neotropical ; and several 

 Neotropical genera, as Heros and Poecilia, are more largely 

 developed here than in any other part of the region. There are 

 also a considerable number of peculiar genera; Petenia, Theraps, 

 and Ne$trop$us (Chromides) ; jffllurichthys (Siluridae) ; Chalci- 

 nopsis (Charadriiidae) ; Characodon, Belonesox, Pseudoxiphophorus, 

 Platypcecilus, Mollienesia, and Xiphophorus (CyprinodontidaeX 

 A few peculiar Antillean forms are also present ; as Agonostoma 

 (Mugilidae) ; Qambusia and Girardinutys (Cyprinodontidae). The 

 oibher families represented are Percidae (1 genus) ; Pristopomatidae 

 (2 gen.) ; Gobiidae (1 gen.) ; Clupeidae (2 gen.) ; and Gymnotidae 

 (1 genus). 



On the whole the fish-fauna is typically Neotropical, but with 

 a small infusion of Nearctic forms. There are a considerable 

 proportion of peculiar genera, and almost all the species are 

 distinct from those of other countries. The predominant family 

 is that of the Cyprinodontidae, represented by 12 genera; and 

 the genus Heros (Chromidae) has here its maximum development, 

 containing between thirty and forty species. Dr. Giinther con- 

 siders that a number of sub-faunas can be distinguished, corre- 

 sponding to some extent, with the islands into which the country 

 would be divided by a subsidence of about 2,000 feet. The 

 most important of these divisions is that separating Honduras from 

 Costa Rica, and as it also divides a very marked ornithological 

 fauna we have every reason to believe that such a division must 

 have existed during the latter portion of the tertiary epoch. 

 We shall find some farther evidence of this division in the 

 next class. 



Insects. The butterflies of various parts of Central America 

 and Mexico, having been largely collected, offer us some 

 valuable evidence as to the relations of this sub-region. Their 

 general character is wholly Neotropical, about one half of the 



VOL. II. 5 



