MELONIA, FORAMENIFERA. 23 
disk convex on both sides, and covered with tubercles ; cir- 
cumference margined with unequal radiating lobes ; septa 
transverse, and imperforate ; aperture somewhat lateral, and 
distinctly developed. 
Siderolites caicitrapoides. Plate II. fig. 10. Found in 
the Mountain of St Peter at Maestricht. 
This genus is known only in the fossil state. 
Genus IV.—DISCORBIS. —Lamarck. 
Generic Character.—Shell discoidal, spiral, multilocular, 
with simple partitions ; all the volutions visible, exposed, 
and contiguous ; transverse septee numerous, and imper- 
forate. 
Discorbis vesicularis. Plate I. fig. 11. 
TRIBE II.— RADIOLACEA. 
Shells discoidal, with a central spire, and elongated radia- 
ting cells, which extend from the centre to the circumference. 
Genus V.— PLACEN TULA. — Lamarck. 
Generic Character. — Shell orbicular, convex above and 
beneath, multilocular; aperture oblong, narrow, disposed 
like a radius in the inferior disk, or in both. 
Placentula Astricans. Plate II. fig. 13. 
Genus VI.— ROTALIA. — Lamarck. 
Generic Character. — Shell orbicular, multilocular, spiral, 
convex or conical above; flat, radiated and tubercular 
beneath; aperture marginal, trigonal, and resupinate. 
Rotalia trochidiformis. Plate II. fig. 16. Internal struc- 
ture. Plate ILI. fig. 12. 
TRIBE IiI.—SPHERULACEA. 
Shell globular, spherical, or oval, with volutions mutually 
embracing, or with cells contiguous, and forming a tunic. 
The shells of this tribe are multilocular and minute, of a spheroidal or 
oval form. Some are destitute of any other cavity than that of their cells, and 
with the volutions mutually enveloping each other; others are provided with 
a particular internal cavity, consisting of a series of elongated, narrow, and 
contiguous eells, forming, by their union, a covering, which surrounds the 
eentral eavity. 
Genus VII. — MELONIA. — Lamarck. 
Generic Character.— Shell sub-spherical, multilocular, 
