REVIEWS 
Cambrian Brachiopoda. By CHARLES D. Watcotr. Monograph 
of U.S. Geological Survey, No. LI, Part I, Text, pp. 1-872; 
Part II. Plates pp. 1-363, Plates I-CIV. Washington, 1912. 
Rarely, perhaps never, has there been published a paleontological 
monograph so complete in every detail as this great work on the Cam- 
brian brachiopods by Dr. Walcott. The work is not merely a monograph 
of the Cambrian brachiopods of North America, but of the Cambrian 
brachiopods of the world, and it includes also those lower Ordovi- 
cian species which are close allies of, and doubtless descendants from, 
the Cambrian forms. The treatment of the fossil forms is both geological 
and biological. A large amount of geologic and geographic data, of 
great value to students of geology, is brought together in most con- 
venient tabular form. Many pages are devoted to a record of every 
locality throughout the world from which Cambrian brachiopods have 
been secured, giving lists of species, not only of the brachiopods but of 
other fossil forms which are associated with them, and giving also the 
stratigraphic relations. 
The zodlogical treatment of the fossil organisms is very complete. 
The various structural details are described with great care. Every line 
of investigation which gave promise of throwing light upon the relation- 
ships of these early forms was assiduously followed, and the results are 
clearly recorded. 
The number of Cambrian species fully described and illustrated in 
the monograph is 477, with 59 varieties. These are distributed among 
44 genera and 15 subgenera, which are grouped under 14 families belong- 
ing to the three orders Atremata, Neotremata, and Protremata. The 
lower Ordovician species discussed are 64 species with 3 varieties, 
belonging to 14 genera and 3 subgenera, and 6 families. Nearly 77 per 
cent of the Cambrian species are members of the two inarticulate orders 
Atremata and Neotremata, and the more specialized order of the articu- 
lata, the Telotremata, is not represented. In a survey of this vast 
array of comparatively simple types of brachiopods, a large proportion 
of which are of small size, sometimes even minute, many series of which 
are notably uniform in their general configuration, the astonishing thing 
is that so great an amount of generic and specific differentiation has been 
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