42 
Vorticialis. — Shell discoidal, spiral, multilocular ; whorls contiguous, not apparent out- 
wardly ; septa transverse, imperforate, not extending from the centre to the peri- 
phery : aperture marginal. 
Plate XX. Fig. 15. V. strigilata. [Icon. — Enc. Method. PI. 470, fig. 2, a. 6.] 
15. (a) Ditto magnified. 
Nummulites. — Shell lenticular, thin towards the margins; spire internal, discoidal, mul- 
tilocular, covered by many thin plates ; exterior margin of the whorls folded in two, 
extending from each side of the shell to the centre, and uniting : chambers very 
numerous, small, alternate ; septa transverse, imperforate. 
Plate XXII. Fig. 9. N. complanata. Fossil. [Mr. J. D. C. Sowerby’s Cabinet.] 
Nautilus. — Shell discoidal, spiral, multilocular, sides simple; whorls contiguous, 
the last covering the others. Chambers numerous ; septa transverse, concave 
from the side of the aperture ; disk perforated by a tube ; and the margins very 
simple. 
Plate XX. Fig. 16. N. umbilicatus. 
II. Shell multilocular, the septa indented at the borders. 
AMMONEATA. — 5 Genera. 
Septa sinuous, lobed, and indented at the circumference, united at the inner surface of the shell, and 
articulating with it by means of indented sutures. 
Ammonites. — Shell discoidal, spiral; the whorls contiguous, and the whole of them ap- 
parent; the internal partitions articulated by sinuous sutures: septa transverse, 
lobed and indented at the circumference, their diskswithout a syphon, but pierced 
by a sort of marginal tube. 
Plate XXII. Fig. 10. A. armatus. Fossil. (Sowerby’s Min. Conch.) [Mr. G. B. Sowerby’s Cabinet.] 
Orbulites. — Shell sub-discoidal, spiral; the whorls contiguous, the last covering the 
others, and the internal partitions articulated by sinuous sutures : septa trans- 
verse, lobed at the circumference, and perforated by a marginal tube. 
Plate XXII. Fig. 11. O. striata. Fossil. [British Museum.] 
Ammonoceratites. — Shell corniform, arched, semicircular; partitions articulated by si- 
nuous, ramose, indented sutures: septa transverse, sinuous, lobed and indented at 
the circumference. Tube or syphon marginal, not piercing the septa. 
Plate XXII. Fig 12. A. glossoidea. Fossil. [Icon. — Bowdich’s Elements of Cone.] 
Turrilites. — Shell spiral, turreted, multilocular; the whorls contiguous, and the whole 
apparent; the partitions articulated by sinuous sutures : septa transverse, lobed, 
and indented at the circumference. Aperture rounded. 
Plate XXII. Fig. 13. T. costulata. Fossil. [Mr. G. B. Sowerby’s Cabinet.] 
