VII.] SPECIES AND SPACE. 165 



and exclusively an inliabitant of fresh water is as jQt 

 known to be found in distant continents, yet that in 

 several other instances fishes identical in species (though 

 not exclusively fresh-water) are found in the fresh waters 

 of distant continents, and that very often the same genus 

 is so distributed. 



The genus Mastacemhclus belongs to a family of fresh- 

 water Indian fishes. Eight species of this genus are 

 described by Dr. Giinther in his catalogue.^ These forms 

 extend from Java and Borneo on the one hand, to Aleppo 

 on the other. Nevertheless, a new species (if. cryptacan- 

 tlius) has been described by the same author,^ which is an 

 inhabitant of the Camaroon country of Western Africa. He 

 observes : " The occurrence of Indian forms on the West 

 Coast of Africa, such as Periophthalmus, Pscttus, Masta- 

 cembclas, is of the highest interest, and an almost new 

 fact in our knowledge of the geographical distribution of 

 fishes." 



Ophioccphalns, again, is a truly Indian genus, there being 

 no less than twenty-five species,^ all from the fresh waters 

 of the East Indies. Yet Dr. Giinther informs me that 

 there is a species in the Upper Nile and in AVest Africa. 



The Acanthopterygian family {Labyrinthici) contains 

 nine fresh- water genera, and these ar^e distributed between 

 the East Indies and South and Central Africa. 



The Carp fishes (Cyprinoids) are found in India, Africa, 

 and Madagascar, but there are none in South America. 



Thus existing fresh-water fishes point to an immediate 



' See his Catalogue of Acantliopteiygiaii Fishes in the British Museum, 

 vol. iii. p. 540. 



2 Proo. Zool. See. 1867, \k 102, and Ann. Mag. of Nat. Hist. vol. xx. 

 p. 110. 



^ See Catalogue, vol. iii. p. ■169. 



