TRILOBITES. 725 
Bronteus lunatus.] 
Family BRONTEID. 
Genus BRONTEUS, Goldfuss, 1839 (em. 1843), 
Brontevs Lunatus Billings, 1854. 
Bronteus lunatus BILLINGS, 1855. Geol. Surv. Canada, Rept. Progress, p. 338. 
Bronteus lunatus BILLINGS, 1853. Geology of Canada, p. 188, fig. 187. 
. Bronteus lunatus is the earliest representative of the genus known in America, 
and the only species yet described from the lower Silurian rocks of this country. 
The characters of the species were given at length by Billings, his originals coming 
from the Trenton limestone of Ottawa where, as said by him, it is not of infrequent 
occurrence. In the Geology of Canada (op. cit.) an excellent wood-cut of an entire 
individual was given. 
The specimens from Minnesota, while all more or less incomplete, agree 
throughout with the Canadian species and we have therefore introduced Billings’ 
Fig. 43.—Bronteus lunatus, after Billings. ° 
figure as more satisfactory to the student than any which might be derived from 
the material before us. The latter consists of a somewhat broken individual having 
the parts together from the Trenton limestone near Spring Valley, Minnesota (No. 
4071 of the Museum collection), a cranidium from the Galena limestone at Wykoff 
(Mr. Ulrich’s collection), and a fine external impression of a pygidium from the same 
locality (Dr. Robbins’ collection). 
Throughout the species of Bronteus there is a certain homogeneity in structure 
which renders the generic group more compact and sharply delimited than is usual 
among the trilobites. But few suggestions of a division of the genus have been 
made and only one of the proposed subordinate generic terms has met with even a 
partial acceptance. This is T’hysanopeltis, one of Corda’s terms, designed to include 
species with marginal spines on the pygidium, and which has demonstrated its title 
to recognition, since the group has proven to possess a quite definite stratigraphical 
value as a structural variation prevailing in Hercynian faunas. 
In B. lunatus the various parts were not involved in the development of any 
unusual characters. The species possess a short axis on the pygidium, which shows 
