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ORDER IV. —CEPHALOPODA. 
THIS Order is separated into Three Divisions, viz. Polythalamous Cephalopoda, Mono- 
thalamous Cephalopoda, and Naked Cephalopoda. 
Division I POLYTHALAMOUS CEPHALOPODA. 
Shell multilocular, completely or partially enveloped, situated on the posterior part of the body of 
the animal, often adhering. 
This Division contains Seven Families — Orthocerata, Lituolata, Cristata, Sphaerulata, 
Radiolata, Nautilacea, Annnoneata. 
L — Shell multilocular, the septa simple, not shewing any divided sinuous sutures on 
the internal surface of the shell. 
ORTHOCERATA ,5 Genera. 
Shells straight, or nearly so ; not spiral. 
Belemnites. — Shell straight, an elongated cone, formed of two distinct and separable 
parts. The external sheath solid, full at the upper part, with a conical cavity ; the 
internal a conical nucleus, pointed, chambered transversely through its whole 
length, multilocular: the chambers perforated by a syphon in the centre. 
Plate XXI. Fig. 10. B. subconicus. Fossil. (Nautilus belemnita. — Gmel.) [Brit. Mus.] 
Orthocera. — Shell straight, or slightly arched, subconical, striated on the outside by 
numerous longitudinal ribs: chambers formed by transverse septa, perforated by 
a central, or marginal tube. 
Plate XX. Fig. 5. O. raphanus. (Nautilus raphanus. — Gmel.) 
5 (a) Ditto magnified. 
Nodosaria. — Shell elongated, straight, or slightly curved, subconical, nodular; nodules 
globular, very smooth. Chambers formed by transverse septa, perforated in the 
centre, or near the margin. 
Plate XX. Fig. 6. N. radicula. (Nautilus radicula. — Gmel.) [Icon. — Enc. Method. PI. 465, fig. 4 5. ] 
6 (a) Ditto magnified. 
Hippurites. — Shell cylindrical, conical, straight, or rather curved, multilocular, septa 
transverse. An internal lateral channel, formed by two longitudinal, parallel, 
obtuse and converging ledges ; the last chamber furnished with an operculum. 
Plate XXII. Fig., 1. H. curva. Fossil. [Mr. J.D. C. Sowerby’s Cabinet.] 
Conilites. — Shell conical, straight, slightly bent; sheath thin, distinct from the nucleus, 
which it contains. Nucleus sub-separable, multilocular, transversely divided by 
septa. 
Plate XXII. Fig. 2. C. pyramidata. Fossil. [Mr. J. D. C. Sowerby’s Cabinet.] 
