1054 The American Naturalist. [December, 
and cross references to upwards of 2,500 species, necessitating about 
10,000 citations. All the literature relating to North and South Amer- 
ican fossil Brachiopods is recorded in this synopsis, and 2,053 valid 
species are recognized, of which 1,922 are North American, and 1,859 
are restricted to the Paleozoic. It is estimated that 6,000 Paleozoic 
species have been described for the whole world ; therefore about one- 
third of the number occur in North America. 
In the American Mesozoic, a marked scarcity of Brachiopods exists, 
since but 49 species have been recorded, and many of these are rare. 
The Cenozoic representation is even smaller, there being but 14 species. 
In the North American Cambrian, there are 116 known species, with 
319 in the Ordovician, 311 in the Silurian, 662 in the Devonian, while 
the Carboniferous representation declines to 478. In America, the 
class practically became extinct with the close of the Paleozoic, for but 
11 species are known from the Triassic and 13 from the Jurassic. Dur- 
ing the Ordovician, the increase was extremely rapid and all the essen- 
tial types occur near the base of the system in the Calciferous. The 
culmination of the class was attained during the Devonian. 
Under the geographic distribution of Brachiopods, it is stated that 
537 species had great areal or horizontal dispersion, and 121 species 
are common to North America and other continents. The specific dis- 
tribution increases with ordinal rank, so that while 25 per cent of the 
Atremata had dispersion, the Neotremata show 27 per cent; and the 
higher orders, the Protremata and Telotremata, each show 32 per cent. 
The order Atremata is best developed in species and genera in the Cam- 
brian and Ordovician systems; the Neotremata in the Ordovician ; the 
Protremata in the Ordovician, Silurian, and Devonian ; and the Telo- 
tremata in the Devonian. The climax of differentiation is, therefore, 
chronologically related to phylogenetic or sequential origin. But 8 
genera are known to pass from the Paleozoic to the Mesozoic. There 
are in all 327 Brachiopod genera, 227 of which are Paleozoic. 
After the discussion and tables illustrating the geologic development 
and geographic distribution of the American fossil forms, the author 
presents a chapter on Brachiopod terminology, in which all the 
current descriptive terms are defined. The biologic development is 
then taken up in detail for the separate orders and for special important 
features, as the protegulum, prodeltidium, cardinal areas, articulation, 
deltidium, spondylium, etc. The morphology of the brachia is dis- 
cussed in a separate chapter prepared for this work by C. E. Beecher. 
_ The various schemes of classification applied to the Brachiopods are 
taken up chronologically, and the strong and weak points of each are 
