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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, Ammoneata. 
I. — Shell multilocular , the septa simple, not shelving 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.] 
Ortiiocera. — 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 &.] 
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.] 
