336 REPORT OF NATIONAL MUSEUM, 1892. 



Beptilia. — All reptiles are air-breathers, and a large part of them are 

 strictly land animals. Many are amphibious, and some are habitually 

 aquatic in their habits. Among aquatic reptiles are the Hydrophidae 

 and some of the Ohelonia, which live in marine waters, and others ot 

 the latter order which live in fresh waters. The Crocodilia also usually 

 inhabit fresh waters and the shores of the same, but they frequently 

 range into the saline waters of estuaries and lagoons. The greater 

 part of all living reptiles of aquatic habits, however, are found in fresh 

 waters, and therefore fossil reptilian remains referable to living fami- 

 lies are regarded as more likely to indicate a nonmarine than a marine 

 origin for the formation containing them. 



The abundance and great variety of known fossil reptiles show that 

 the class is only partially represented by all those now living. Fur- 

 thermore, most of the extinct reptiles differed so much from any living 

 kinds that comparatively little inference may be drawn as to the char- 

 acter of their respective habitats by a consideration of those of living 

 reptiles. The character of the habitat of those of extinct reptiles must 

 be learned mainly from their osseous structure and their dentition ; but 

 in the case of those whose aquatic habitat is thus determined, the 

 marine or nonmarine character of the waters in which they lived is 

 rarely indicated. Therefore, while a great, and doubtless the greater, 

 part of the preserved remains of extinct reptiles were intombed in non- 

 marine sediments, whether those sediments were deposited in brackish 

 or fresh waters must usually be learned, if learned at all, from other 

 evidence than that which is furnished by the remains themselves. 



Batrachia. — In their larval, gill-bearing condition all Batrachians 

 are denizens of fresh waters, usually those of pools and marslies. A 

 few of them retain their gills and fresh-water habitat during life, but 

 most of them become air-breathers. A part of these become denizens 

 of the dry land, but the remainder continue to live in the palustral 

 habitat in which their larval stage was passed. Therefore it is assumed 

 that batrachian fossil remains are much more likely to be found in 

 strata of fresh, than of marine, or even of brackish, water origin. 



Pisces.* — Because all fishes have aqueous respiration it is desirable 

 for the present purpose to review the whole class by families. The 

 general facts concerning the habitat of each family are well exhibited 

 by the following tabular arrangement of their names, the three columns 

 of the table representing marine, brackish, and fresh waters, respec- 

 tively. The occurrence of the name of a family only in the left hand 

 column indicates that no representative of it is known in any other 

 than marine waters; and in case the name occurs only in the right 



* The classification here used is that of Dr. Theodore Gill in his arrangement of 

 the families of fishes as published in Smithsonian Miscellaneous Collections No. 247, 

 pp. 1-25 and personally revised hyhiin fortius essay. Dr. Gill has long had in hand 

 an elaborate revision of this classification; but that which is here presented is deemed 

 sufficient for the illustration of these discussious. 



