
REVIEWS. 609 
liable to be differently understood, and he admits (p. 72) that the pla- 
a the peculiar character of which he takes for his guide in defining 
the five groups of the MD is **a structure not universally char- 
ah of the class." these exceptions and gaps taken into ac- 
count, in addition to the Bots of the placental characters to one 
Sex, is not the Cerebral system as likely to lead to a natural grouping of 
the orders of Mammalia as one based on the reproductive organs? 
From what we have stated it must not be supposed, by those who have . 
ing from the study of the reproductive organs, for, on the contrary, while 
their peculiar structure, and the development of the embryo an and i 
tion to the parent, forms the basis of his division of the class into three 
subclasses, and the structure of the placenta that of the five secondary 
groups of Ea principal subclass; he also gives other characters common 
to each , and in his summary of the orders he brings together their 
principal pieno elements, and discusses their relations from other 
stand points, for an understanding of which we must refer the reader to 

Without farther comments — other than to state that it is our belief that 
the orders of the birds ‘lik: require farther confirmation before they are 
generally adopted = ornithologists, and (—— that the orders of the is 
Reptilia and Amphibia are mainly those now com — received — we | 
give the poti £s of his second Province, pan SAUROPS 
lass I. Brrps (Aves), he divides into three pice ce SAURURJE, 
containing only the extinct form, Archeopteryx; (2) RATITÆ, containing 
the Ostriches, Emeus, Apteryx, etc.; (8) CaRINAT.E, containing all the 
ordinary birds. 
Class II. RrPTILES (Reptilia), he divides into four orders of living and 
five of fossil forms:— (1) CRocopirLrA (Crocodiles, Alligators, and their 
n amel 
allies); (2) LACERTILIA (Lizards, Blindworms a eleons); (3) 
HIDIA (the Sn 4) CHELONIA (the Turtles and Tortoises). Th 
five orders represented only by fossils are the ICHTHYOSAURIA, the I- 
OSAURIA, ~ DICYNODONTIA, the PTEROSAURIA and the DINOSAURIA. 
rd Province, m stein Mn iud the classes of Am- 
phibians ie Fishes, is arranged as follows: 
Class I. AMPHIBIANS paese scm orders:— (1) Umoprra (the 
Newts, Salamanders, Sirens, ete.); (2) Barracnta (the Frogs and 
Toads); (3) Gym Mete (the Czecilians, etc.) ; (4) LABYRINTHODONTA 
(fossil forms’ 
Class II. Yum (Pisces). Six orders :—(1) Drexor (containing only the 
singular ** Mud fishes," Lepidosiren and Rhinoeryptis) ; (2) ELASMOBRANCHIT 
(Sharks, Skates, and Chimeras); (3) GaNormrr (Sturgeons, — 
Dogfish (Amia), ete.); (4) TErLEosrEI (the ordinary ** Bony” fishes) ; (5) 
ARSIPOBRANCHII (Lampreys, etc.) ; (6) PHARYNGOBRANCHIL ae Aa 
by the single genus Amphiozus). 
AMER. NATURALIST, VOL. III. 77 

