CEPHALOPODA. 71 
Actinoceras bigsbyi.] 
Family ACTINOCERATID A. 
Genus ACTINOCERAS, Bronn, 1537. 
AcTInocERAS BIGSBYI Stokes, 1840. 
PLATE XLVIL. FIGS. 15—17. 
Actinoceras bigsbyi STOKES, 1840. Trans. Geolog. Soc. London, sec. ser., vol. v, p. 707, (fig. in ditto, 
vol. i, pl. xxv, figs. 1—3. 1824). 
Compare Ormoceras tenuifilum HALL. Paleontology of New York, vol. i. p. 55, pl. xv, fig. 1-le; pl. xv1, 
figs. 1-le; pl. xvii, figs. la, b. 
Considerable uncertainty must long remain in regard to the specific values of 
the various orthoceran shells illustrated by Bigsby in 1824 and obtained from 
Thessalon and other islands in lake Huron.* Of the several plates of illustrations 
representing these, names were given only to the Huronias, and those by Stokes. It 
was only with the publication of Stokes’ paper, cited above, that names were pro- 
posed for some, but not all of the examples of Actinoceras figured by Bigsby. All of 
these are weathered interiors, and there is an evident agreement among them all, 
including also those referred to the genus Ormoceras, notwithstanding the fact that 
later investigations have tended to indicate a more recent age to the species there 
termed Ormoceras backi and O. bayfieldi. Actinoceras bigsbyi is safely enough an early 
Trenton form, with many evident points of relationship to Hormoceras tenuifilum 
Hall, of the Black River limestone of New York. The two are undoubtedly conge- 
neric, though the New York specimens are not often retained in such a manner as to 
show the endosiphon and its radial canals. 
The Minnesota collections have furnished but two or three specimens which 
may be referred to this species, one exposing in vertical section twelve air-chambers 
in a length of 105 mm., with a width at the upper end of 36 mm. and at the lower 
end of 25 mm. The other specimen consists of an internal cast of four air-chambers, 
showing that the sipho is very large and excentric, extending quite to the margin. 
The great width, however, is at the lower surface of each air-chamber, its diameter 
greatly diminishing at the upper surface. The greatest width of the siphonal beads, 
extending thus into the chambers and resting with a broad base upon the septa, is 
fully two-thirds the diameter of the shell. The endosiphonal walls are thick 
especially where the beads are broadest, and the endosiphon seems to vary in size 
with its position in the shell. The casts of this tube show a wrinkled surface and 
bases of radial branches. 
Formation and locality——I1n the Trenton limestone at Minneapolis, and at Garrick’s quarry, near 
Rochester, Minnesota. - 
Museum Register, No. 23, 159. 
*The title of Bigsby’s paper is: ‘*Notes on the Geography and Geology of Lake Huron.” ‘Trans., ete., vol. 1, pp. 
177-209. 
