NATJTILID^. 
177 
tom. ii.), p. 105, pi. xxiii. f. 4. — 1883. Koninckiocems ingens, 
Hyatt, Proc. Boston Soc. Nat. Hist. vol. xxii. p. 295.] 
Char. Shell thick, discoid, consisting of three or four slightly 
embracing whorls, aU exposed in a wide and deep umbilicus, which 
has a small central perforation. The sides of the umbilicus slope 
inwards, and its edge is defined by an obscure angulation, which 
in the adult shell rises into a coarse ridge on the body-chamber. 
The periphery in the young shell is simply rounded, but as growth 
proceeds it becomes obtusely angular along the median line, the 
angulation again becoming almost obsolete on the body-chamber of 
full-grown individuals. The section in the young shell is wider 
than high, the ratio of the two diameters being about as 21 : 18 ; 
in the adult the height and width (owing to the prominence of the 
lateral angles) are nearly equal. The body- chamber occupies about 
one half of the last whorl. 
The septa are moderately distant, being about 8 lines apart upon 
the sides of an adult shell, where the diameter is inches. On 
the periphery the septa bend slightly forwards in the direction of 
the aperture, while on the dorsal side they make a very deep back- 
wardly-directed sinus, first making a very sharp (forwardly-directed) 
angle at each edge of the furrow caused by the overlapping of the 
whorls. There are indications of an “ inner lobe ” in one of the 
specimens in the Collection (“ Sowerby Collection”; the specimen 
numbered 43865 a). The siphuncle is nearly central, but a little 
nearer the inner than the outer margin. The surface of the test 
is marked with fine, transverse lines of growth. 
Remarks. I am quite in agreement with Prof. M‘Coy as to the 
propriety of uniting the Nautilus ingens of Martin with the Nau- 
tilus pentagonus of Sowerby. Prof. M‘Coy supports his opinion in 
the following terms : — 
The examination of a great number of large specimens induces 
me to propose the union of Nautilus pentagonus (Sow.) with this 
species [JN. ingens'], because out of a great number of specimens 
with rounded periphery, some have the inner whorls convex on the 
sides, and the outer ones fiattened, and there are all gradations 
between the broadly rounded periphery of the true N. ingens and 
the keeled exterior of the N. pentagonus ; but it curiously happens 
that the two widest extremes which I have seen are at the two 
ends of one large fragment from Closeburn, which in itself would 
set the question completely at rest ; further, this latter specimen, so 
strongly keeled in its unseptate portion, shows the impression of 
simply rounded whorls of the spire on its inner margin.” 
This latter observation of M‘Coy’s is completely corroborated by 
TART II. N 
