54 
PROCEEDINGS OF THE ACADEMY OP 
AcTEON (Solidula) attennuta. 
Shell small, elongate ; spire elevated ; volutions (number unknown) depres- 
sed, or but slightly convex, separated by a shallow, but distinct suture. Sur- 
face ornamented by numerous small punctate striae, usually less than the 
spaces between, and numbering about fourteen on the second turn ; sometimes 
there is on the body whorl a much smaller stria between each two of the 
others ; while near the base of this volution the striae are stronger than above, 
and more distinctly punctate. Lip and columella unknown. Length about 
•57 inch ; breadth 17th inch ; apical angle convex, divergence 18°. 
As our specimen is not in a condition to show the collumella, we are left in 
some doubt respecting its generic relations, but its form and surface markings 
'are similar to those of species usually referred to the genus Acteon. 
Locality and position. — Yellow-stone river, formation No. 4 and 5 blended 
together. 
Helicoceras? tortus. 
Our specimen of this species is a fragment, consisting of one septate volution 
of the spire. This evidently belonged to a sinistral conical shell, composed (at 
any rate during a part of its growth) of rounded whorls, which are coiled in 
an ascending spiral, so far out of the same plane as ,to be disconnected by a 
free space equalling about one-third the diameter of each succeeding whorl be- 
low. The umbilical cavity left within, is, at its aperture, less than the diameter 
of the largest volution ; while the whorls increase in size, so as nearly to double 
their diameter each turn. The surface is ornamented by two rows of rather low 
nodes, passing round the lower outer side (the apex of the spire being above) 
of the whorls, — and small, but distinct annular costas, which of. en bifurcate at 
the nodes. 
The siphuncle is very small, and in the specimen before us presents the re- 
markable peculiarity of gradually changing its position in passing from the 
smaller to the larger extremity of the fragment before us. That is to say, — at 
the smaller end of the specimen, it occupies exactly the middle of the dorsal, or 
outer side, but in passing round it gradually curves upwards, so that by the 
time it reaches the larger end, it comes out on the summit of the whorl. Con- 
sequently, if it goes on in this way, another turn of the spire would bring it 
on the inner or umbilical side, — a third on the underside, and the fourth again 
on the dorsal or outer side. It is also worthy of note that the lobes and 
saddles of the septa, and to some extent the nodes, followed the peculiar curve 
of the siphuncle, so that it would seem the whorls not only form an ascending 
spiral curve, but are, as it were, at the same time, twisted in such a manner as 
to change the relative positions of the dorsal and ventral sides. 
The septa are provided with six lobes and six saddles, the larger of which are 
profoundly sinuous and variously branched. The dorsal lobe is comparatively 
small, and ornamented at the extremity by two nearly equal branches, each of 
which is subdivided into from three to five small divisions with sinuous margins ; 
above this there is a small lateral branchlet on each side, the right hand one 
of which is bifid. The superior lateral lobe is considerably larger than the 
dorsal lobe, and deeply divided by its auxiliary saddle into two large unequal 
spreading branches, of which the one on the ventral side is somewhat longer than 
the other, and provided at the extremity by two nearly equal spreading bifid 
branchlets and several smaller digitations ; the other principal division is less 
deeply divided at the extremity into two unequal parts, the terminal or longer 
of which is bifid : the margins of the main branches, as well as of the body of 
the lobe, are also provided with several subordinate divisions with sinuous edges. 
The inferior lateral lobe is somewhat smaller, but in other respects scarcely 
differs from the superior lateral lobe. 
The dorsal saddle is nearly as large as the inferior lateral lobe, but less spread- 
ing above, and narrower, as well as more oblique at its base ; while its extre- 
mity is profoundly divided, by its auxiliary lobe, into two subequal tripaitite, 
[March^ 
