22 CRETACEOUS AND TERTIARY FISH. 



DESCRIPTION OF SPECIES.' 



Class PISCES. 



THE FISHES. 



Cold-blooded aquatic vertebrates breathing by means of gills 

 not purse-shaped, but attached to cartilaginous or bony gill- 

 arches. Skull with lower jaw. Limbs developed as fins, rarely 

 wanting. Body usually covered with scales, bony plates or horny 

 appendages, sometimes naked. Median line of body with one 

 or more fins composed of cartilaginous rays joined by membrane 



(The Leptocardii (Lancelets) and Cyclostomes (Lampreys), 

 usually to be considered with all fish-like vertebrate faunas, are 

 not known from any undoubted fossil remains, and comprise but 

 a small number of existing forms. The opinions of many writers 

 vary as to the value of the different sub-classes embraced in the 

 present class, though most all agree as to the status of the lance- 

 lets and lampreys. I accept five, as the Elasmobranchii, Holo- 

 cephali, Dipnoi, Cross>opterygia and the Actinopteri. At the 

 present time only the Elasmobranchii and Actinopteri are rep- 

 resented by existing types within the limits of New Jersey, 

 though it is probable that some Holocephali may yet be found 

 off our shores in deep water. The Elasmobranchii and Holo- 

 cephali are, however, very abundant among the remains in our 

 Cretaceous beds, and the former represent about half the entire 

 number of fossil fishes known from that formation. 



Sub-Class ELASMOBRANCHII. 



SHARK-LIKE FISHES. 



Teeth distinct. Jaws distinct from skull, joined to it by sus- 

 pensory bones. Gill-openings five to seven slits on each side of 

 pharynx. Membrane bones of head undeveloped, except some- 



1 Bv Henry W. Fowler. 



