

1891.] Recent Literature. 813 
The work is necessarily, from its brevity, synoptic in its treatment 
of the subject, and as such is especially adapted to instruct persons 
_ engaged in active life, whose time for reading is limited. To such 
persons we can recommend the work, as expressing in a brief space 
the results of recent research in a field of the greatest interest to all 
students of mankind or of our own part of it—E. D. Cope. 
æ 
Boulenger on Rhynchocephalia, Testudinata, and Croco- 
dilia.?—In this book of 300 pages we have another valuable result of 
the labors of Dr. Boulenger, which will be of great utility to the 
students of the Reptilian orders named. The very full collections at 
the disposal of the author enable him to settle many questions of 
specific characters that have awaited elucidation, and to assign to their 
proper places in the system many forms which have been named. 
system adopted is clear, and expresses the present state of our knowl- 
edge. For many of its good points the. author is indebted to Dr. 
George Baur, whose recent researches in this field have been of great 
value. Dr. Boulenger has used Dr. Baur’s observations with judg- 
ment, attaching values to them in accordance with their merits. We 
think he has undervalued the character of the mutual attachment of 
the plastron and carapace. On the other hand, the peculiarity of the 
nuchal bones has enabled Baur to distinguish the Dermatemydidæ 
from the Emydidæ. We do not now give as high a rank to the Athecæ 
as does Boulenger, nor would we abolish the suborders, as is proposed 
by Baur, but have adopted an intermediate course. 
Dr. Boulenger reaches a -remarkable conclusion as to the relations 
of the Trionychidæ with broad alveolar surfaces for crushing, to those 
with acute edges of the jaws. He finds that species of India, China, 
and Africa present individuals with both kinds of structure, which are 
otherwise undistinguishable, except by a few correlated characters. 
He thinks that the facts indicate a dimorphism in such species, one 
form being piscivorous and the other conchivorous. He has not found 
- any young individuals with broad grinding alveolar surfaces, and sus- 
pects that that modification is acquired by the animal’s entering on a 
diet of Mollusca, and that it is maintained by persistence in it through- 
out life. The genus Platypeltis thus becomes a modification of Trionyx. 
e This is certainly a remarkable proposition, and it ought not to be 
difficult to prove or disprove it by observations on our Zytonyx ferox, 
the only North American species supposed to present constantly broad 
and flat alveolar surfaces. 
? Catalogue of the Chelonians, Rhynchocephalians, and PA in the British 
Museum By G. A. Boulenger. Published by the trustees, 1 




