402 ZOOLOGY. 
d. Trichechide. 
e. Sirenidia. 
Rytinide, Halichoride, Manatide, Dinotheride. 
VI. Ceraczga. 
Heterodontide, Delphinide, Physeteride, Balenidae. 
VII. Marsupratia. 
a. Carnivora. 
Thylacinide, Didelphide, Dasyuride. 
b. Insectivora. 
Peramelide. 
c. Herbivora. 
Phalangistide, Phascolomyide,Macropodide (Halmaturide). 
VIII Epvenvara. 
a. Tardigrada. 
Bradipodide, Megatheride. 
b. Edentata proper. 
Manide, Myrmecophagide, Orycteropodide, Dasypodide. 
c. Monotremata. 
Kchidnide, Ornithorhynchide. 
A glance at the actual and terrestrial mammalian fauna of North 
America shows a scarcity of the types which we have placed at the bottom 
of the class: the two great groups of Epenrata and Marsvupiatia have 
each but one species, both confined to the warmer part of the continent. 
The Pachydermata are represented by a single species also, not taking into 
consideration the introduced species, the horse, the ass, and hog. The 
Ruminantia are distributed into eight genera, seven of which comprise but 
one species, the introduced not included. The Rodentia are the most 
numerous: they form twenty-one or twenty-two genera, and count from 
eighty to ninety species ; the rodents, it must be observed, are among the 
smallest mammals, and therefore strike the attention less than either the 
ruminants or pachyderms. Insecrivora, twenty to twenty-five in number, 
are arranged into six genera. The Carwivora, the number of which is a 
little above thirty, are distributed into fourteen genera, several of which 
have only one species. The viverrine carnivora: are almost completely 
absent. If future investigations shall increase the number of North Ame- 
rican mammals, it cannot be but in favor of the rodents mostly: that 
group, therefore, may be considered as the most numerous in North Ame- 
rica; next the carnivora proper; next the insectivora, then ruminants. 
The reasons for such proportions must be sought for in the physical condi- 
tion of the continent: the small number of grass feeders is a very remark- 
able fact, and doubtless in direct relation with the proportion of carnivora. 
Thus America, although the continent of vegetation, has not received a 
proportional number of herbivora, showing that the equilibrium between the 
different orders of animals is more important than that of the vegetable and 
animal kingdom. 
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