NATURAL SCIENCES OF PHILADELPHIA. 
55 
deeply sinuous branches. The lateral saddle is very nearly of the same size and 
form as the dorsal lobe, but less oblique, and a little more deeply divided by its 
long auxiliary lobe. 
The greater transverse diameter of our specimen is 2-43 inches ; do. of um- 
bilicus, -65 inch ; diameter of larger end of the whorl 1-04 inch ; do. of the 
smaller end -74 inch; diameter of the siphuncle at the larger extremity -6 inch. 
The peculiar twisted character of the volutions in this shell led us to suspect 
it may be found, when better specimens are obtained, to constitute a distinqt 
genus from any Cephalapod hitherto described. For the present, however, we 
refer it provisionally to the genus to which it appears most nearly related. 
Locality and position. — Great Bend of the Missouri, lower part of No. 4, general 
section. 
TURRILITBS (HeLICOCERAS) COCHLEATDS. 
Shell sinistral, very thin, and composed of rounded, nearly or quite contiguous 
whorls, which gradually increase in size from the smaller to the larger extre- 
mity; umbilicus slightly wider than the diameter of the largest whorl. Surface 
ornamented by numerous small rather irregular bifurcating, annular costae, 
which first pass obliquely backwards and outwards from the umbilicus above, 
then curve so as to cross the dorsum obliquely downwards and forwards, but 
on reaching the lower side, they curve backwards again, in approaching the 
ventral side. There are also two rows of obscure, flattened, or depressed oval 
nodes, one of which passes round nearly exactly over the siphuncle, which 
occupies the middle of the outer side of the whorl, while the other is placed 
less than one-fifth of the circumference of the whorl lower down. 
The septa are rather distant, and divided into six lobes and six saddles, which 
are a little unsymmetrical, in their subordinate details, but about of the same size 
and general form on opposite sides of the siphuncle. The dorsal lobe is small, and 
ornamented at the extremit}^, by four small branches, the two terminal of which 
are a little larger than the others, slightly dissimilar, and each provided witii 
five or six unequal digitations ; the other two divisions are not exactly opposite, 
differ slightly in form, and are each armed with about from three to five or six 
unequal digitate points : above these principal terminal divisions, there are 
also along the body of the lobe a few small alternating lateral pinnules. 
The superior lateral lobe is greatly larger than the dorsal lobe, and very 
deeply divided into two great, subequal, spreading branches, of which the one 
on the ventral side is a little larger than the other (especially on the side of the 
whorl below the siphuncle), and unequally subdivided into three bifid branchlets, 
the two terminal of which are much larger than the third, and each ornamented 
by several small unequal, projecting points, the other main branch is divided 
into two principal, bifid branchlets with many smaller sinuosities and digitations. 
The inferior lateral lobe is somewhat smaller than the superior, but in other 
respects very similar. 
The dorsal saddle is small, very oblique, much contracted at its base, and 
divided above into two unequal variously subdivided, sinuous branches. The 
lateral saddle is not so oblique, but does not otherwise differ materially from 
the dorsal saddle. 
Our specimen consists of a little more than half a volution, the greatest 
transverse diameter of which is 2-34 inches; breadth of umbilicus -75 inch. 
Diameter of the volution at larger end, which is a little oval, -73 inch by -64 
inch ; do. of smaller end, which is very nearly circular, -54 inch. 
It is not easy to determine, from our specimen, whether this species is most 
nearly related to the genus Turrilites or Helicoceras. In the rounded and com- 
parative slender form of its whorls, as well as the large size of its umbilicus, it 
is more like the latter genus ; while the fact that the volutions are nearly or 
quite in contact, as is shown by an impression left on the matrix, would seem 
to indicate that it must belong to the genus Turrilites. It is probable, however, 
1858.] 
