ACTDsOCERATID^. 
205 
Horizon. Xiagara Group (Weulock). 
Locality. Drummond Island, Lake Huron. 
Eepresented by two specimens, one presented by Dr. J. J. Bigsby, 
F.R.S., the other transferred from the Huseum of Practical Geology. 
1824. Huronia ohliqua, Stokes, Trans. Geol. Soc. ser. 2, vol. i. pt. ii. 
explanation of pi. xxyiii. f. 4; and p. 203, Species iv. of Bigsby. 
1840. Huronia.) sp., Stokes, Trans. Geol. Soc. ser. 2, vol. v, pt. hi. 
p. 710, pi. Lx. f. 3. 
1806. Orthoceras (Huronia')^ sp., Barrande, Syst. Sil. de la Boheme, 
vol. ii. Texte hi. 1874, p. 743, pi. ccxxxi. f. 3 (after Stokes, loc. 
cit.). 
Sjj. Char. Of this species the siphuncle only is kuown, though 
in several examples fragments of the septa are attached to it, and 
infold each segment up to the poijit where the most inflated part 
begins, from whence they arched upwards to the shell-wall. 
The most marked feature in this species is the obliquity of the 
siphuncular segments to the vertical axis L A very peculiar struc- 
tui-e, to which attention has already been directed, is also observ- 
able in the segments, viz. for about half their contour they have a 
subturbinate form, which viewed in profile may be aptly compared 
with the figure known in architecture as an ogee, or sigmoid 
moulding ; but in the other half they have a subglobular form. 
This singular asymmetry is best seen in a vertical section passing 
exactly through the centre of each of the two components of the 
segment, and the difference in their outline is then very plainly 
demonstrated. (Fig. 28.) 
^ This is seen also in Actinoccra.% and is plainly attributable to the eccentric 
position of the siphuncle, whose elements, lying between the septa where these 
slope upwards to the shell-wall, are thus deflected from the horizontal position 
The accompanying figures illustrate these two positions of the siphuncle. 
Huronia obliqua, Stokes. 
Fig. 31. 
