CEPHALOPODA. 799 
Onoceras minnesotense.] 
indications of a linear or thickened oval scar extending from the inner margin of 
the, siphonal beads along the major diameter of the septum to near the inner 
dorsal margin. 
Fig. 10.—Vertical median section of O. minnesotense showing the form of the siphonal beads. x 1.6. 
The external surface is covered with numerous low longitudinal ribs, thirty- 
five or forty in number on the later portions of the shell. Among a number of 
specimens representing this species there are none of the body chamber. The 
septate portions afford no satisfactory indication of the expansion which charac- 
terizes the genus Oncoceras; still the material presents many similarities to the 
species described by Whiteaves* as Cyrtoceras manitobense, from the Lower Silurian 
at many localities in Manitoba. The latter possesses a somewhat similar curvature 
of the septa, though a deeper concavity and a greater obliquity ; and it also has a 
similar external ornamentation. Whiteaves’ figures indicate a species with very 
sight arcuation and a decided expansion of the tube toward the aperture, and 
nearly the entire extent of the swelling is septate, the body-chamber occupying but 
a small part of it. It would seem wiser for the present to refer such shells to 
Oncoceras as they must be regarded as differing notably from typical forms of 
Cyrtoceras. The Minnesota specimens are hence thus referred, though they all 
lack the body-chamber. 
Formation and locality.—In the Galena limestone at Hader, Stewartsville, Mantorville, Pleasant 
Grove and Lime City, Minn. A single fragment of the apical portion of a shell having the aspect of the 
other but with the septa closer together is from the Hudson River horizon at Granger, Minn. 
Museum Register, Nos. 258, 4106, 8294, 8295, 8296. 
Oncocrras tycus, Hall, 1861. 
PLATE LVIII, FIGS. 1—3. 
Orthoceras lyewm HALL. Rept. Supt. Geol. Sury. Wisconsin, p. 45. 
Shell arcuate, with an arc of short radius on the ventral curve and a much 
*Trans, Royal Soc. Canada, vol. vii, sect. iv, p. 80, pl. xiii, figs. 8, 4; pl. xv, fig. 4. 1889. 
