202 
NAUTILOIDEA. 
appertain to the shape and proportions of the siphuncular segments, 
nothing hut fragments of the shell being known. 
In the present species the lower two thirds of each segment is of 
a cylindrical form, slowly increasing in diameter and forming a more 
or less inflated rim at the top. 
The latter occupies about ^ of the height of the segment, and the 
ratio of the vertical to the transverse diameter is about as 17 : 19. 
As the specimens are all more or less imbedded in the matrix, it is 
very difiicult to obtain accurate measurements. At the base of each 
segment there is a constriction which indicates the place of insertion 
of the septa, remains of which are here seen, and they are observed 
to he extremely thin and fragile. About six of the siphuncular 
segments are preserved in the specimen figured by Stokes. The 
measurements of the largest of these are : — vertical diameter 1 inch 
8 lines ; transverse diameter 1 inch 7 lines. 
Remarks. In the specimens of this, and in fact of all the examples 
of Huronia, the shelly structures have been replaced by orbicular 
chalcedony (“ beekite ”), and the interspaces between the endo- 
siphon and the walls of the siphuncle are often filled with chalcedony 
of the ordinary amorphous kind. This process of silicification has 
extended to all the fossils of the Niagara Group of Drummond 
Island, and generally throughout the Lake Huron region, and they 
have thus been preserved from the usual solvent agencies. The 
frequent absence of the shell and septa in Huronia can therefore 
only be accounted for on the suj^position that those parts were 
broken to pieces immediately after the death of the animal, being 
too fragile to withstand the concussions to which dead shells are 
subjected on the sea-bottom. 
Horizon. Niagara Group (Wenlock). 
Locality. Drummond Island, Lake Huron. 
Represented by a fine series of specimens, some of which were 
presented by Dr. J. J. Rigsby, F.R.S. 
Huronia^ vertebralis^ Stokes. 
1824. Huronia vertehralis, Stokes, Trans. Geol. Soc. ser. 2, vol. i. 
pt. ii. “ Explanation of Plates,” pi. xxviii. tf. 2 & 6, and p. 202, 
Species i. of Rigsby. 
1851. Huronia vertehralis, Hah, in Rep. on the Geol. of the Lake 
Superior Land District, by Foster and Whitney, pt. ii. p. 221^ 
pi. xxxiv. f. 1. 
1857. Orthoceras Canadense, Rillings, Geol. Surv. of Canada, Rep. of 
Progress for the years 1853-56, p. 321. 
