PALEONTOLOGY: C. D. WALCOTT 
101 
CAMBRIAN TRILOBITES 
By Charles D. Walcott 
SMITHSONIAN INSTITUTION, WASHINGTON, D, C. 
Received by the Academy, January 31,1916 
The writer has assembled data to aid in clearing up some of the prob- 
lems of formations of the Appalachian region by a careful comparison 
of portions of their contained faunas with those of the Mississippi Val- 
ley, the Cordilleras, and other localities. No thorough study and com- 
parison of many genera of the Cambrian faunas has been made, though 
collections from many outcrops have been in the writer's possession for 
years, awaiting the opportunity to make these studies so necessary in 
his work on the Cambrian Trilobites. 
Two new families of trilobites are proposed, Menomonida^ and Nor- 
woodidae, and seven new genera: Menomonia, Millardia, Dresbachia, 
Norwoodia, Saratogia, Vanuxemella, and Hanhuria; 46 new species and 
three new varieties are described, with 19 earher described species and 
several genera. One of the marked features of the paper is the de- 
scription of a number of genera of the order Proparia: Menomonia, 
Millardia, Dresbachia, and Norwoodia. These, taken in connection with 
the genus Burlingia, described in a previous paper (Cambrian Trilo- 
bites, Smithsonian Misc. Coll., 53, No. 2, 1908, p. 14) estabHsh the 
existence of a strong group of the order in Cambrian time. 
The stratigraphic position of the Weeks formation is changed from 
Middle to Upper Cambrian, and the problem of whether the Conasauga 
formation of the Coosa Valley and adjoining areas shall be restricted 
to the Upper Cambrian, and the Middle Cambrian beds there given 
a formation name, is left for further detailed study. 
The discussion and comparison of the Crepicephalus group of trilo- 
bites is particularly interesting, including a comparison of 17 different 
species, 10 of them new species, 3 new varieties, and two undetermined 
species. The five plates of illustrations of this large trilobite also pre- 
sent many new and interesting features of the animal, now so long 
extinct. 
The details of this investigation with fifteen plates continuing 280 
figures will be found in Smithsonian Misc. Coll., 64, No. 3, 1916. 
