292 
NAUTILOIDEA. 
Nautilus Atlas, Whiteaves. 
1840. Nautilus elegans, d’Orbigny, Pal^ontologie Fran^aise (Terrains 
Cretac^s), vol. i. p. 87, pi. xix. {Not of J. Sowerby.) 
1850. Nautilus eleyans, d’Orbigny, Prodrome de Pal^ontologie Strati- 
grapliique, vol. ii. p. 145. {Not of J. Sowerby.) 
1853. Nautilus elegans, Sharpe, Description of the Fossil Remains of 
the Mollusca found in the Chalk of England, Mon. Pal. Soc. pt. i. 
Cephalopoda, p. 12, pi. iii. f. 3, pi. iv. f. 1. {Not of J. Sowerby.) 
1876. Nautilus Atlas, M hiteaves, Ceol. Surv. of Canada, Mesozoic 
Fossils, vol. i. pt. i. p. 17. 
Sp. Char. Shell inflated, broadly rounded on the periphery, which 
makes a continuous arch with the sides and imparts a semilunate 
outline to the whorls when seen in section. The greatest breadth 
of the whorls is therefore a little above the umbilical region. 
Umbilicus closed. The septa are rather distant, being (type speci- 
men) I 5 inches apart where the height of the whorl, measured 
from the umbilicus to the median line of the periphery, is 3.;J inches. 
Siphuncle situated considerably above the centre of the septa. Test 
ornamented with rather strong, prominent, rounded ribs, separated 
from each other by interspaces equal to about half the diameter of 
the ribs. The latter make a broad forwardly-directed curve on the 
sides of the shell, and a broad and shallow sinus on the periphery. 
Owing to the lateral compression undergone by some specimens 
this sinus appears very deep in them, but in uncompressed speci- 
mens, of which there are a few in the Collection, the sinus is always 
shallow. The ribs leave their mark upon the cast in the form of 
faint plications. 
Remarks. The above description is drawn up chiefly from 
d'Orbigny’s figured type, but there is in the British Museum a fairly 
good example (No. C. 1027) from the same horizon and locality 
(Craie Chloritee, Rouen) as d'Orbigny’s specimen. The Museum 
possesses also a good number of English specimens, a few of which 
are fairly well preserved (see Nos. C. 573, a, b,c, and 38683 ; one 
of these (No. C. 573) preserves its proper shape. They all exhibit the 
characteristic inflated form of the present species, by which it may 
be primarily distinguished from N. elegans, J. Sow., though to this 
feature must be added the closed umbilicus and the position of the 
siphuncle (approaching the peripheral border), all which characters 
separate it from Sowerby’s species. 
It may be observed that d’Orbigny’s type specimen has had the 
matrix removed from the last exposed chamber since it was figured 
in the Pal. Frang. (pi. xix. ff. 1 , 2), and the specimen now shows 
the position of the siphuncle. 
