Book Excerpt Entitled, "Lituites Robertsoni"

Hall, Geol. Rep. Wis 1861 p 38

LITUITES ROBERTSONI, ^ (n. s.)

Description. Shell discoid, consisting of three or four volu-
tions. Volutions ventricose, very slightly embracing, rounded
on the sides and somewhat flattened on the middle of the

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back, the ventral sides being slightly concave, giving a very
obtusely quadrangular section to the volution, the lateral di-
ameter of which is a little greater than the dorso-ventral di-
ameter.

Septa concave, numerous, these being on the back, about six
in the space equal to the lateral diameter at the same point.
Siphuncle small, situated on the back of the volution, outer
chamber very gradually expanding.

Surface marked by obscure undulating folds, which com-
mence upon the vertical side of the volution, and arching back-
wards unite with those from the opposite side in low ridges
which are bent backwards in a broad sinus upon the dorsum.
Lines of growth parallel to the undulations cover the entire
surface.

This species differs conspicuously from L. undatus of the
Trenton limestone of New York in the much more closely ar-
ranged septa, those of that species being less than half the
number in the same space where the diameter of the volution
is the same.

Geological Formation and Locality. In the "Buff limestone"
of the Trenton limestone group, at Beloit, Wisconsin, and
Rockford Illinois.

The species is dedicated to T. D. Robertson, Esq., of Rock-
ford.