Creruatoropa.] UPPER PALOZOIC MOLLUSCA. 559 
enlarging, their edges exposed in the very deep narrow umbilicus ; first whorl an oblique, obtusely pointed cone, 
reticulated by strong spiral and transverse striee (two or three of which seen on the edge of the umbilicus gave 
rise to the species V. bistrialis of Phillips) ; the spiral strize disappear on the large whorls which are almost 
smooth, or marked with slight lines of growth; mouth transversely reniform, obtusely rounded at the sides, 
and having a deep semielliptical sinus in the middle of the edge when perfect, as also indicated by the lines 
of growth. Septa moderately numerous, evenly convex, with simple transverse edges ; siphuncle large, central. 
83 
Diameter of moderate specimen two inches one line, proportional width of mouth 3, antero-posterior dia- 
meter of mouth *, diameter of umbilicus =. 
Some of the internal casts shew a small mesial ridge in parts of the periphery. The umbilicus is a little 
wider in proportion in the young shells. 
Position and Locality —Very rare in the dark carboniferous limestone of Poolwash, Isle of Man; not very 
uncommon in the carboniferous limestone of Lowick, Northumberland ; rather rare in the black beds over the 
main limestone of Derbyshire; very rare in the limestone of Kendal, Westmoreland. 
NaAvTILUS INGENS (Aart. Sp.) 
Ref. and Syn.= Conch. Naut. A. ingens Martin, Pet. Derb. t. 31. = Nautilus id. Phill. Geol. York. Vol. IT. 
t. 18. f. 4+. pentagonus Sow. Min. Con. t. 249. f. 1. 
Dese.—Discoid, gibbous, of about four whorls (rarely more than one and half preserved), about one 
half of each whorl of the spire concealed by the inyolutions; umbilicus wide, usually with sloping sides, and 
then defined by an obtuse angulation from the sides of the shell, or (in other specimens, or other parts of 
same specimen) moderately convex and undefined; volutions thick, sides either very convex or slightly 
flattened ; periphery either broadly rounded or obtusely carinate along the middle; edge of the mouth with 
a rounded, angular sinus in the middle; septa simple, moderately convex ; siphon nearly central, a little 
nearer the inner than the outer margin. Dimensions of small specimen, diameter five inches, proportional 
diameter of last whorl =, diameter of umbilicus 4, width of last whorl “. Shell having the surface marked 
with fine, obsolete, transverse lines of growth. Last few septa, with a diameter of one inch and half, four 
lines apart; with a diameter of four inches, one inch apart. Adult diameter about nine inches. 
The examination of a great number of large specimens induces me to propose the union of Nautilus 
pentagonus (Sow.) with this species, because out of a great number of specimens with rounded periphery, 
some have the inner whorls convex on the sides, and the outer ones flattened, and there are all gradations 
between the broadly rounded periphery of the true V. ingens, and the keeled exterior of the VV. 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 speci- 
men so strongly keeled in its unseptate portion, shews the impression of simply rounded whorls of the spire 
on its inner margin. 
Position and Locality.—Common, of large size, in the impure limestone of Lowick, Northumberland ; 
common in the red carboniferous limestone of Closeburn, Dumfriesshire; rare in the carboniferous limestone 
of Kendal; rare in the carboniferous limestone of Derbyshire. 
Nautitus Lui1 (Martin). 
Ref. and Syn.= Conch. N. A. Luidi Martin, Pet. Derb. t. 35. f. 1, 2. 
Desc.—Discoid, of two and half gradually increasing whorls, not embracing; (centre pervious;) mouth 
transversely oval; periphery very broad, convex, sides narrow, rounded, sloping rapidly with slight convexity, 
to form the wide umbilicus. Entire surface marked with about thirty-six subequal, narrow, thread-like keels, 
slightly smaller on the sides of the umbilicus, separated by wider, slightly concave, spaces ; about five ridges 
in three lines on middle of body-whorl, at an inch and half in diameter, closer at smaller size, and fewer in 
[easc. 111. ] 4 
