B20 LE SAVAGE 
The variation presented in the ventral valve of this species is 
similar to that shown in the shells described by the writer as 
Virgiana barrandei var. mayvillensis, and V. barrandet var. major 
from the Mayville limestone in Wisconsin. At the time those 
varieties were described the only other known representatives of 
this genus were Virgiana barrandei and a variety of that species 
occurring in the Becsie River (earliest Silurian) formation of 
Anticosti Island, from which it was thought that they might have 
been derived. However, the Virgzana shells from Wisconsin are 
now known to be more closely related to Virgzana decussata than 
to the Anticosti forms. In recognition of this relationship it is ~ 
here proposed to elevate the varieties Virgiana barrandei var. 
mayvillensis and Virgiana barrandet var. major to the rank of species. 
The former differs from Virgiana decussata in having somewhat 
fewer and coarser radiating plications, less numerous concentric 
markings, and usually is relatively wider in the anterior part of 
the shell. Virgiana major is a larger shell than V. decussaia, and 
generally has a much more strongly developed keel-like median 
ridge on the ventral valve. 
Regarding the age of the strata containing these shells in the 
Grand Rapids region Kindle’ says: 
Close comparison between the faunas of the Grand Rapids section and 
those of eastern Silurian sections, owing to the dearth of common species, is 
difficult. The dominance in the lowest (Silurian) fauna of this section of such 
a genus as Conchidium, however, makes it probable that the base of the section 
represents a Silurian horizon not earlier than the Clinton, and probably of early 
Niagaran age. 
This argument is no longer applicable, since instead of belonging 
to the middle Silurian genus Conchidium, the species in question 
belongs to the genus Virgzana, which is an early Silurian genus 
known elsewhere only from strata of pre-Niagaran (Alexandrian) 
age. 
The early Silurian age of the strata containing Virgiana decussata 
in the Grand Rapids of the Saskatchewan and the Hudson Bay 
regions can be shown by their relations to associated strata in dif- 
ferent areas. In the Grand Rapids region the layers containing 
Virgiana decussata are succeeded by strata which contain the fossils 
tk. M. Kindle, op. cit., p. 9. 
