Chap. III. EARLY ATTEMPTS. 18V 



Mammalia. But I hold, at the same time, with other naturalists, that the Batrachia 

 must be separated, as a class, from the true Reptiles, as the characters ■which distin- 

 guish them are of the kind upon Avhich classes are founded. I am also satisfied 

 that the diilerences which exist between the Selachians, (the Skates, Sharks, and 

 Chima^raj,) are of the same kind as those which distinguish the Amphibians from 

 the Reptiles proper, and justify, therefore, their separation, as a class, from the 

 Fishes proper. I consider also the Cyclostomes as a distinct class, for similar 

 reasons ; but I am still doubtful whether the Ganoids should be separated also from 

 the ordinary Fishes. This, however, cannot be decided until their embryological 

 development has been thoroughly investigated, though I have already collected data 

 which favor this view of the case. Should this expectation be realized, the branch 

 of A^ertebrata would contain the following classes : — 



1st Class : Myzontes; with two orders, Myxinoids and Cyclostomes. 



2d Cla.ss : Fishes proper ; with two orders, Ctenoids and Cycloids. 



3d Class : Ganoids; with three orders, Ccelacanths, Acipenseroids, and Sauroids ; 

 and doubtful, the Siluroids, Plectognaths, and Lophobranches. 



4th Class : Selachians; with three orders, Chimoera", Galeodes, and Batides. 



5th Class : Amphibians; with three orders, Cajcili*, Ichth3'odi, and Anixra. 



6th Class : Reptiles; with four orders, Serpentes, Saurii, Rhizodontes, and 

 Testudinata. 



Ttli Class: Birds; with four orders, Natatores, Grallaj, Rasores, and Insessores, 

 (mcluding Scansores and Accipitres.) 



8th Class : Mammalia; with three orders, Marsupialia, Herbivora, and Car- 

 nivora. 



I shall avail myself of an early opportunity to investigate more fully how 

 far these groups of Vertebrata exhibit such characters as distinguish classes, and I 

 submit my present impressions upon this subject, i-ather as suggestions for further 

 researches, than as matured results. 



SECTION II, 



EARLY ATTEMPTS TO CLASSIFY ANIMALS. 



So few American naturali.sts have paid special attention to the classification 

 of the animal kingdom in general, that I deem it necessary to allude to the 

 different principles which, at different times, have guided zoologists in their attempts 

 to group animals according to their natural ailinities. This will appear the more 



