VERTEBRATA. 177 



has been proposed by Dr. Cope ; it is of a most radical character, 

 what nearly corresponds to the Teleostei being divided into 24 

 orders, all with new names. A good account, by Dr. Th, Gill, of 

 the various systems previous to 1873 is given in the 'American 

 Naturalist,' vii. pp. 71 et seq. 



Schmarda (1878) has six subclasses with fourteen orders. The 

 former are Leptocarclii, Cyclostomata, Selachii, " Ganoidea," Te- 

 leostei, and Dipnoi. The last four constitute the subclass Euich- 

 thyes for Glaus, Leptocardii and " Cyclostorni" forming the other 

 two subclasses of his arrangement. 



The orders here adopted are those recognized by Huxley, with 

 the addition of Cuvier's two orders Lophobranchii and Plecto- 

 gnathi, and Muller's order Holocephali. Giinther's arrangement 

 of the families and genera has been generally followed, except 

 that the sequence has been reversed. Some families have only 

 one species in each. 



Without lungs, branchiae only. 



No skull PHARYNGOBRANCHII. 



With a skull. 



No lower jaw MARSIPOBRANCHII. 



With a lower jaw. 

 With free gill-covers. 

 Gills pectinate. 



Without true scales PLECTOGNATHI. 



With true scales. 



Scales horny, overlapping each 



other, &c TELEOSTEI. 



Scales bony, not overlapping. . . GANOIDEI. 



Gills in tufts LOPHOBRANCHII. 



Gill-covers rudimentary ; one branchial 



aperture HOLOCEPHALI. 



Gill-covers absent ; 5-7 branchial aper- 

 tures CHONDROPTERYGII. 



With lungs and branchiae DIPNOI. 



Order I. PHAEYNGOBEANCHII. 



ACEPHALA. MYELOZOA. CIRROSTOMI. ENTOMOCRANIA. ACRANIA. 

 LEPTOCARDII. CEPHALOCHORDA. 



Notochprd persistent. Skeleton membrano-cartilaginous. No 

 skull, brain, limbs, nor heart. Mouth without jaws, surrounded 

 with cirri. 



