330 ©. D. Walcott—New Genus of Cambrian Trilobites 
The succeeding eleven posterior segments appear as though 
formed of a more delicate test than the anterior portions of the 
body, as they are much more flattened and compressed than the 
latter, and the plural grooves are alinost obsolete. The 
or this form the genus Mesonacis is proposed. One other 
species, UO. Howelli, from Central Nevada, will probably be re- 
ferred to it when the thorax and pygidium are found, as the 
head is very closely related to that of I Vermontana. 
The stratigraphic position of M. Vermontana is eleven bhun- 
dred feet from the base of the Georgian Group, in the argillace- 
ous shales at Parker’s quarry, town of Georgia, Franklin coun- 
ty, Vermont, where it is associated with Olenellus Thompson’, 
Protocaris Marshi, Ptychoparia Adamsi, etc. 
1e Georgian Group, in Vermont, consists of one thousand 
feet of magnesian limestone at the base, overlaid by from eight 
thousand to nine thousand feet of argillaceous shales in which 
great lenticular masses of limestone occur that carry a fauna 
similar to that of the shales. The base of the group and also 
its summit is at present unknown, 
In Central Nevada, in an unbroken section, the Potsdam 
fauna, as found in New York and Wisconsin, occurs four thous- 
and feet above the characteristic Georgian fauna, the intervem 
ing strata being entirely formed of limestones. i 
aper now in course of preparation by the writer, Se 
tions will be given , accompanied by lists of fossils, to show the 
relations of the St. John (Paradoxides), Georgian (Olenellus) 
and Potsdam (Dicellocephalus) Groups, or the Lower, Middle 
and Upper Cambrian. , 
In Bulletin 10, of the U. 8. Geological Survey, the subgenus 
Salteria is proposed by the writer to include Concoryphe Bailey's 
Hartt and C. venulosa Salter of the Lower Cambrian. ws @ 
name had been previously given to a genus of trilobites (Mem. 
Geol. Surv. Brit. Organic Remains, Dec. xi, pl. vi) which 0 : 
sitates the substitution of another subgeneric name for the 
species mentioned. Mr, G. F. Matthew (Trans. Roy. A 
Canada, vol. xi, description of pl. i) having proposed the ne 
Bailiella, that will replace Sateria as applied to ConocoryP 
(Bailliella) Baileyi of the St. John Group. 
