54 
NAUTILOIDEA. 
convex side. Septa numerous ; sutures simple. Siphuncle cylin- 
drical, usually near the convex border of the shell, or between that 
and the centre ; rarely near the concave border, as in G. expansum, 
Saemann. The test is ornamented with lines of growth, or, in 
addition to these, with regularly arranged, strong, tubercular folds 
(Silurian and Devonian species) ; or with numerous longitudinal 
ridges, studded with small tubercles (Carboniferous species). — Silu- 
rian to Carboniferous ^ 
Remarks. The history of this genus may be briefly sketched as 
follows : — James de Carle Sowerby was the first to describe a species 
belonging to the genus Gtfroceras under the name of “ Orthocera 
paradoxica ” (placed in this work in the suhgenus Trigonoceras). 
Sowerby, though suspecting that he was dealing with a new generic 
type, was too cautious to institute a new genus for the reception of 
the strange form he was describing. His obseiwations upon its 
affinities are interesting, and as they are not lengthy I here trans- 
scribe them : — 
“ It would perhaps have been proper to constitute a new genus 
of this very remarkable fossil, to be placed between Saatilus and 
Orthocera, but experience has shown us how dangerous it is to form 
genera from such characters as fossils possess, especially when frag- 
ments only are preserved and we have not the whole tribe before us. 
We know of only a short portion of the shell before us ; one end of 
it is but half as wide as the other, and the curvature not more 
than the sixth part of a circle ; therefore if it be an involute shell, 
the inner whorls must be very slender, or the outer one must have 
receded from them with a much less degree of curvature than they 
possess. The genus Spirula is perhaps the nearest approach among 
recent shells to such a form as this fossil might possibly have had 
when perfect : in the present state of our knowledge of its form, 
however, it would seem to be a rather bold assertion to declare them 
of the same genus.” 
In 1829 Hermann von Meyer described some fossil fragments 
under the name of Gyroceratites gracilis \ which consisted of portions 
1 Some authors have cited this genus as originating in the Ordovician Period, 
but this is probably a mistake. It is true that Billings (Report of Progress, 
Geol. Surv. of Canada, for the years 1853-56 (1857), p. 307) described a species 
from the Ordovician of the island of Anticosti under the name of “ Gyroceras 
{Litiiites) magnijicum ” ; but^his specimens were in such a bad state of preser- 
vation that they failed to show aU the generic characters oiGyroceras, and might 
have belonged to Lituites or to Trochoceras. 
^ Nova Acta Acad. Leop.-Carol. vol. xv. pt. ii. p. 73. 
