RELATION OF BIOLOGY TO GEOLOGICAL INVESTIGATION. 343 



Some of the Gasterosteidse are confined to marine waters and others 

 to fresh. Most species are found in brackish waters. 



The Belonidse are mostly marine, some of them ranging into estu- 

 aries and even into fresh water. One genus is of exclusively fresh- 

 water habitat. 



The Scomberesocidse are also mostly marine, some ranging into estu- 

 aries and even into the adjacent fresh waters. 



The Cyprinodontidae are mainly fresh-water tishes, but some range 

 into estuaries and some are denizens of salt waters. 



The Microstonmhe are mainly marine, but one species occurs also in 

 fresh waters. 



Some of the Salmonida- have an exclusively fresh-water habitat, never 

 migrating to salt waters. A large proportion of them migrate from 

 marine to fresh waters for reproduction, but none of the family is 

 wholly con lined to marine waters. 



The Salangidae are typically marine, but some range into estuaries. 



The Elopidie are mostly marine, but some range into estuaries, and 

 one species is found in the fresh waters of Lake Nicaragua. 



Some of the Clupeida? are conhued to marine waters, and at least one 

 species is known only in fresh waters. A large proportion of them, 

 however, range from marine into fresh waters for reproduction. 



The range of habitat of the Dorosomidre is similar to that of the 

 Clupeidse. 



The Siluridae are mainly denizens of fresh waters, but one section of 

 the family is confined to marine waters. 



The Plotosidoe are mostly marine, but some species range into 

 brackish waters and in some cases into fresh Abaters also. 



The Anguillidse all range from marine to fresh waters, returning to 

 marine waters for reproduction. 



The Acipenseridse are usually found in fresh waters, but some of 

 them range down into estuaries and even into waters of full marine 

 saltness. 



The Trygonidie are mainly confined to marine waters, but one sec- 

 tion of the family is peculiar to South American fresh waters. 



The Raiidse are almost exclusively of marine habitat, but some range 

 into estuaries, and they have occasionally been found in waters that 

 are nearly or quite fresh. 



All the Pristidse, with very few known exceptions, are confined to 

 marine waters. One species is found in the fresh waters of Lake Nica- 

 ragua and another in the Philippine islands ranges from marine into 

 fresh waters. 



One species of the Galeorhinidse is also found in Lake Nicaragua 

 and another ranges from marine to fresh waters in the Philippine 

 islands. All other known species are confined to marine waters. 



Of the thirty-nine families mentioned in the foregoing notes as hav- 

 ing representatives in more than one of the three kinds of habitat 

 designated in the table. 28 of them are so generally confined to marine 



