112 
NATJTILOIDEA. 
The difference between the shell-muscles of Codonautilus and 
those of the recent Nautilus strongly] supports the view that the 
two forms are generically distinct, a conclusion already arrived at 
from the great dissimilarity in the form of their shells by such an 
eminent authority as Prof. Hyatt. The subdivision of Nautilus, as 
is well known, was begun long ago by M‘Coy ^ and continued by 
Meek^, the latter of whom expressed his decided opinion that such 
divisions should rank at least as distinct subgenera. 
Coelonautilus cariniferus, J. de C. Sowerby, sp. 
182o. Nautilus cariniferus^ J. de C. Sowerby, Min. Conch, vol. v. p. IdO, 
tab. cccclxxxii. f. 3 (excl. f. 4). 
? 1825. Nautilus bianc/ulatus, J. de C. Sowerby, Min. Conch, vol. v. 
p. 84, tab. cccclviii. f. 2 (two figs.). 
1828. Nautilus excavatus, Fleming, Hist, of British Animals, p. 231. 
1836. Nautilus cariniferus, Phillips, Geology of Yorkshire, pt. ii. p. 232, 
pi. xvii. f. 19. 
1836. Nautilus sulciferus, Phillips, ibid. p. 232. 
1844. Nautilus {Temnocheilus) cariniferus^ M^Coy, Synop. Carboni- 
ferous Foss. Ireland, p. 20. 
1855. Naidilus cariniferus, M‘Coy, British Pal. Foss. fasc. iii. p. 557. 
1889. Calonautilus cariniferus, Foord and G. C. Crick, Geol. Mag. 
dec. iii. vol. vi. p. 494, figs. A-E^. 
[Yg‘^ 1844. Nautilus cariniferus, de Koninck, Descrip, des Anim. Foss, 
du Terr. Carbonifere de Belgique, p. 549, pi. xlviii. ff. 11, a, b, Sc 12. 
1878. Ibid., Faune du Calcaire Carbonifere de la Belgique (Annales 
du jNIus. Roy. d’llist. Nat. de Belgique, tom. ii.), p. 134, pi. xxviii. 
ff. 1-5.] 
Char, “ Discoid, subglobose ; inner whorls half exposed in a 
large umbilicus ; a keel in the middle of each side, and two ridges 
between it and the flattened front.” (Sowerby.) 
Bemarks. The single prominent keel or ridge upon the edge of 
the umbilicus distinguishes this species from C. paucicarinatus, in 
which there is another keel just inside the umbilical hollow. The 
septa in the present species are very slightly sinuous upon the sides 
and periphery ; their distance from each other increases slowly with 
the growth of the shell. In the adult they are 4 lines apart upon 
the sides, where the dorso-ventral diameter is 14 lines. The 
siphuncle is large, and is situated a little above the centre. 
^ Synopsis of the Carboniferous Limestone Fossils of Ireland, 1844. 
2 United States Geol. Survey of the Territories, 1876, vol. ix. p. 490. 
3 The foregoing remarks on the shell-muscles of Ccelonautilus (pp. 109-1 J 2) 
are reprinted from this paper. 
