elegance, number, and variety of the species, which exceed by three times those of their living analogues. The Cerithium giganteum attains a con→ siderable magnitude. Some masses of the Bognor rock are almost wholly composed of a species of Pectunculus. The Ampullaria (Tab. 38, fig. 7) abounds at Grignon, and is commonly in a beautiful state of freshness. You will recollect that in most of the carnivorous species the aperture of the shell is channelled. (Tab, 38, figs. 2, 3, 4, 5.)

TAB. 39.-FRESH-WATER SHELLS OF THE PARIS BASIN. Figs. 1, 2. Bulimus conicus. 3, 4. Cyclostoma mumia. 5. Lymnea effilea. 6, 7, 8. Planorbis.

FRESH-WATER TERTIARY SHELLS.-It has al

ready been observed, that the shells of the mollusca

which inhabit fresh water, possess characters by which they may be distinguished from the marine species. This small selection from the fresh-water beds of Paris will serve to elucidate my observations. The general appearance of these shells will bring to your recollection the species which inhabit our ponds and rivers; particularly the large thin snail (lymnea, fig. 5) and the discoidal shells (planorbis, figs. 6, 7, 8); while figs. 3 and 4 (cyclostoma) resemble a species often found on the banks of lakes. At Headon Hill, and at Binstead in the Isle of Wight, the clay and limestone are filled with the remains of several species of planorbis and lymnea.

30. NUMMULITES, AND OTHER CEPHALOPODA. -Several species of nautilus abound in the tertiary strata; those inclosed in the septaria, or indurated argillaceous nodules, of the London clay at Highgate, Sheppey, and Bognor, possess considerable beauty, and admit of being cut in sections, which admirably display the internal structure of the original. I shall, however, defer an explanation of their mechanism to the subsequent lecture, when analogous fossil genera will come under our notice. My observations will now be restricted to an interesting division of the Cephalopoda (as those mollusca are termed whose head is surrounded by the organs of motion, or feet), called Foraminifera, which comprehends many genera, and several hundred species, the greater part being microscopic,

and analogous to the recent forms which inhabit the Mediterranean. These bodies are entirely distinct from the testaceous habitations of snails, periwinkles, &c.: they are, in truth, not an ex. ternal, but an internal apparatus; and it is supposed, that, in addition to their having served as a point of attachment and support to the soft body of the animal, they acted as a buoy, which could be made heavier or lighter at pleasure, and by which the animal was enabled either to sink

Fig. 1. Transverse section of a Nummulite. 2, 3. Nummulites, with the external plate partially removed.

or swim. The fossil called Nummulite (from its resemblance to a coin) affords a beautiful illus

tration of the structure of these bodies.

It is

of a lenticular, discoidal form, and varies in size from a mere point to an inch and a half in diameter. The outer surface is generally smooth, and marked with fine undulating lines. On splitting the shell transversely, it is found to consist of several coils, which are divided into a great many cells or chambers by oblique partitions (Tab. 40, fig. 1), apparently having no communication with each other, but which the animal, probably, had the power of filling with fluid, or air, through foramina or pores; whence the name of the order. To Dr. George Hall (physician to the Sussex Hospital), I am indebted for the specimens exhibiting this structure, which I now place before you (Tab. 40); they are from the limestone formed of nummulites, held together by calcareous cement, which constitutes the foundation rock of the Great Pyramid of Egypt, and of which that structure is in part composed. Strabo alludes to the nummulites of the pyramids, under the supposition that they are lentils which had been scattered about by the workmen, and become converted into stone.* This polished, silicious pebble, presented me by the Marquess of Northampton, is also from Egypt; the markings on the surface are sections of the inclosed shells. The nummulite is one of the most widely diffused of fossil shells, its remains forming whole chains of

*See Wilkinson's Manners and Customs of the Ancient Egyptians, vol. ii. p. 371.

calcareous hills: it is not confined to the tertiary, but occurs also in the secondary formations, and constitutes immense beds in the Alps and Pyrenees. The blue clay at Bracklesham and at Stubbington, and the calcareous sandstone of Emsworth and Bognor, in Sussex, abound in nummulites. In North America, the limestone which occurs near Suggsville, and forms a range of hills about 300 feet in height, is entirely composed of one species of nummulite. This limestone is porous, and contains spheroidal cavities formed by the decomposition of the organic remains,*

31. CRUSTACEA AND FISHES.-Crabs and lobsters, of species related to the recent, several of which are described by MM. Brongniart and Desmarest, in their beautiful work on Fossil Crustacea, have been found in the clay of Highgate, and in the Isle of Sheppey. The external configuration of the shell or crustaceous covering of these animals being in conformity to the viscera which they inclose and are intended to protect, the naturalist is able, by an accurate acquaintance with the characters of the living species, to point out the relation or difference of the fossil, even though the carapace or buckler alone remains; and the size and situation of the heart, stomach, &c. may thus be readily determined. This remarkably fine crab

* Nummulites Mantellii of Dr. Morton. See Synopsis of the Organic Remains of the Cretaceous Group of North America. 8vo, with numerous plates. Philadelphia.