‘CEPHALOPODA. 191 
The orthocerata are the most abundant and wide-spread shells 
of the old rocks, and attained a larger size than any other fossil 
shell. A fragment of an orthoceras, in the collection of Mr.- 
Tate of Alnwick, is a yard long, and 1 foot in diameter, its 
original length must have been 6 feet. Other species, 2 feet in 
length, are only 1 inch in diameter at the aperture. 
Sub-genus. 1. Cameroceras, Conrad (= melia and thoracocerag, 
Fischer ?). 
Siphuncle lateral, sometimes very large (simple ?). 
Casts of these large siphuncles were called hyolites by Hichwald. 
27 species. Lower Silurian—Trias? North America and 
Europe. 
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R.A 
WINS 
Fig. 54. Actinoceras.* Fig. 55. Ormoceras. 
2. Actinoceras (Bronn), Stokes. Siphuncle very large, in- 
flated between the chambers, and connected with a slender 
central tube by radiating plates. 6species. Lower Silurian— 
Carb. ; North America, Baltic, and Brit. 
3. Ormoceras, Stokes. Siphuncular beads constricted in the 
middle (making the septa appear as if united to the centre of 
each). 3 species. Lower Silurian—Deyon; North America. 
This sub-genus yery much resembles, if it is not identical with, 
the last mentioned. 
4. Huronia, Stokes. Shell extremely thin, membranous or 
horny? Siphuncle very large, central, the upper part of each 
joint inflated, connected with a small central tube by radiating 
plates. 3 species. Lower Silurian. Drummond Island, Lake 
Huron. 
Numerous examples of this curious fossil were collected by Dr. 
Bigsby (in 1822), and by the officers of the regiments formerly 
* Fig. 54. Actinoceras Richardsoni, Stokes. Lake Winipeg. (Diagram reduced #.) 
Fig. 55. Ormoceras Bayfieldi, Stokes, Drummond Island. (From Mr, Stokes’ paper, 
Geol, Trans,) 
