196 
NAUTILOIDEA. 
genus, but he could add nothing to what ho had previously stated 
respecting its structural characters. Professor 'Whitfield, however, 
met with a specimen of Discosorus belonging to the Collection of 
the Geological Survey of Wisconsin, in which septa were preserved 
in contact with the siphuncle, thus making clear the affinities of the 
organism. 
Added to this are two examples of Discosorus in the British Mu- 
seum, both of which have the septa preserved, and one of them 
(fig. 26 A) has a considerable part of the shell remaining. 
The large proportionate size and nummuloidal character of the 
siphuncle bring Discosorus into close relationship with ActinoceraSy 
from which, however, it is differentiated by features which, taken 
together, are of sufficient importance for generic distinction. 
Discosorus would seem to bear the same relationship to Aciinoceras 
(perhaps as a brevicone form of it, as suggested by Barrande) that 
Piloceras bears to Endoceras. 
Both Discosorus and Piloceras are short, curved forms, having 
structural affinities with long straight ones. 
Horizon. J^iagara Group (Wenlock). 
Localities. Drummond Island, Lake Huron ; Niagara. 
Well represented in the Collection by numerous specimens, one of 
them having formerly belonged to Dr. Mantell's collection, and 
another having been transferred from the Museum of Practical 
Geology. 
Discosorus conoideus. Hall. 
1824. Columns composed of circular discs &c., Bigsby, Trans. Geol. 
Soc. ser. 2, yol. i. p, 204, pi. xxx. ff’. 4, 6, ? 3 (?iot ff o, 7). 
1851. Discosorus conoideus, HaU, in Deport on the Geol. of the Lake 
Superior Land District, by Foster and Whitney, pt. ii. p. 222, 
pi. xxxiv. ff. 2, 3 
1852. Discosorus conoideus, Hall, Pal. of New A'ork, yol. ii. p. 99, 
pi. xxyiii. ff. 13, a, b, c. 
1863. Discosomis {Orthoceras') conoideus, Billings, Geol. of Canada, 
p. 335. 
1874. Orthoceras? {JDiscosQrus') conoideus, Barrande, Syst. Sil. de la 
Boheme, yol. ii. Texte iii. p. 750, pi. ccxxxii. ff. 1, 2 (after Bigsby), 
pi. ccccxxxyii. ff. 19-22 (teste Billings), pi. cccclxxiy. ff. 7, 8. 
1882. Discosorus conoideus, Whitfield, Geol. Siiry. of Wisconsin, 
yol. iy. pt. iii. ; Paleeont. p. 299, pi. xx. f. 6. 
Bp. Char. These must necessarily be confined mainly to a 
^ I have not seen these figures, as, in the copy of the Eeport to which I have 
had access, pi. xxxiv. is wanting. 
