NUCLEUS. 71 
broad, flat, its inner edge straight, denticulated; operculum 
testaceous, semicircular, sub-spiral, with an articulating process 
on the inner edge. Obs. This genus of fresh-water shells differs 
from Nerita in the minuteness of the denticulation of the colu- 
mella, as well as in the characters mentioned in our observations 
upon the latter genus. N. spinifera. (Clithon, Montf.) fig. 325. 
N. virginea, fig. 324. N. perversa, Lam. (Velates, Montf.) fig. 326. 
NERITOP'SIS. Gray. Fam. Neritacea, Lam. Descr. Sub-glo- 
bose, thick, cancellated; spire short, composed of few rapidly 
increasing whorls; aperture transverse, sub-orbicular; outer-lip 
thickened within; columellar-lip thick, rather flat, with a large 
rounded notch in the centre of its inner edge. Obs. This genus 
most nearly resembles Nerita, from which it differs in the pecu- 
liar notch in columella. N. granosa, fig. 331. 
NO’BIA. Leach. Order. Sessile Cirripedes, Lam. This genus 
resembles Pyrgoma, Auct. consisting of a conical paries sup- 
ported upon a funnel-shaped cavity in the madrepore, but 
differs in its operculum, which consists of two valves; whereas 
that of Pyrgoma hasfour. N. grandis, fig. 29. 
NODOSA‘RIA. Lam. and Orthocera, Lam. have been united by 
Sowerby, under the first name. Fam. Orthocerata, Lam. and 
Bl. Deser. straight chambered, elongated; chambers more or 
less ventricose; septa perforated by a central siphon. Obs. This 
genus consists only of fossils found in sub-appenine tertiary 
beds. N. equalis, fig. 465. 
NO’GROBS, Montf. A fossil, appearing from the figure and 
description to resemble Belemnites. 
NO'NION. Montf. A genus of microscopic Foraminifera. 
NONIONINA. D’Orb. A genus of microscopic Foraminifera. 
NOTREMA. Rafinesque. A shell described as composed of three 
integral valves,concerning which De Bl. puts the query “ne 
seroit-ce pas plutot une Balanide mal observée ?”’ 
NOVACULINA. Benson. (Novacula, a razor.) Fam. Solen- 
acea, Lam. Descr. Equivalve, inequilateral, transversely elon- 
gated, external ligament communicating with the interior of the 
shell by an oblique channel; beaks prominent; hinge line nearly 
straight, with one narrow, curved, cardinal tooth in one valve, 
entering between two similar teeth in the other; siphonal scar 
long, extremities of the shell gaping; epidermis thin, light 
brown, folding over the edges and connecting the dorsal margins. 
Hab. Jumna Gumti and Ganges. Fig. 63. 
NUCLEOBRANCHIA’TA. Bl. The fifth order of the second 
section of Paracephalophora Monoica, Bl. Fam. 1. Nectopoda, 
containing Carinaria; Fam. 2. Pteropoda, containing Atlanta, 
Spiratella, Argonauta. 
NU’CLEUS. (A kernel.) Anything around which matter is gath- 
ered. The nucleus of shells is the first formed part; the first 
