with Dr M'Bain, dredged up the nests of Pontobdella in the Firth of Forth. Sir J. Dalzell had figured these nests and the young in his "Powers of the Creator," vol. ii. plate 1, and well described them in that work.

Referring to Mr Peach's description of the Nidus of Numertes gracilis, Dr Wright stated that the nests of several annelides might be found in the pools near Seafield, the eggs of which had been hatched under his care, and he described the progress of development in the embryo. He stated that at one stage the embryo of the annelid exactly resembled that of Cydippe pomiformis, formerly described by him to the Society.

IV.—Notice of Snakes and Lizards from Old Calabar. By GEORGE LOGAN, Esq., W.S.

During the year 1857, the missionaries in Old Calabar connected with the United Presbyterian Church in Scotland, transmitted to some of the Fellows of the Royal Physical Society a considerable number of specimens of snakes and lizards, and of other interesting objects in various departments of natural history. Of the reptiles a portion were sent to Dr J. E. Gray, of the Zoological Section of the British. Museum, with a request that he would examine and name them, that they might be described and submitted to this Society; and if there were any duplicates among them which would be of service to the Museum, they might be retained. Dr Gray acknowledged receipt of the specimens transmitted to him, but he seems to have overlooked or forgotten the conditions attached to their transmission, as in the spring of last year (1859) he, upon personal application at the Museum, only returned six of them named, without any notice of the remainder. He was then written to, reminding him of the terms upon which the reptiles were sent to him, and that it was desirable that a list and description of them should be submitted to this Society, but no answer was received to this communication. The British Museum Catalogue, and the Proceedings of the Zoological Society of London, have furnished, however, to some extent the information awanting. The following notice by Dr Gray appears in these Proceedings, Part xxii., March 1858, page 154:-" Mr Logan kindly

sent to me for examination a number of snakes and other reptiles which had been collected by the missionaries in Old Calabar. Among several very interesting species I observed a new genus of the family Boida, which I have great pleasure in laying before the Society, more especially as it appears to be the indication of a new tribe in that curious family.

"This animal belongs to the second section of the family which is thus characterised:

"II. Tail very short, not, or only very slightly, prehensile. Head indistinct, short.

"It is entirely distinct from the tribes Cylindrophina, Carinina, and Tortricina, and therefore I propose to form for it a tribe (Calabarina) by itself, having the same characters as the genus.

66

"Calabaria.

8-8

Head small, short, rounded in front, the same size as the body; muzzle depressed, rounded; labial shields flat, ; the hinder small, front moderate; rostral shield high, large, triangular; frontal shields, three pairs, band-like, subsimilar, followed by a band-like shield continued from side to side, which has behind it a small subtrigonal shield on each side, with a central large triangular shield between them on the crown. Eyes surrounded by scales, on the upper edges of the upper labial shields, and the outer edges of the fourth and fifth frontal plates, and with one ocular shield in front, and two smaller behind the eyes; loreal shield single, small; pupil circular. Nostril lateral, between two small nasal shields. Body cylindrical. Scales broad, triangular, polished, rather sunken and subrugose in the centre. Ventral shields very numerous, band-like, transverse, about half as wide as the diameter of the body. Vent small, with a single preanal shield. Spurs large, distinct. Tail short, as thick as the body, blunt, and rounded at the end. Subcaudal shields broad, band-like, one-rowed, like the ventral shields.

"I think it probable, when some other specimens have been examined, that the band-like shield extending across from the upper edge of each eye will be found to be composed of three shields like the band behind it, which are here united into

one band; and then the head shields will lie thus:-three pair of band-like frontal, two smaller triangular superciliary shields over each eye, having in the middle between them two triangular parietal shields.

"Calabaria Fusca (pl. xiv.)

"Dark brown, some of the scales yellowish, scattered singly or in groups on the back and sides; ventral shields grayish. Sides of the belly with a few unequal yellow spots.

Length, 36 inches; diameter, 1 inch. Hab. Old Calabar, West Africa. (Geo. Logan, Esq.) "Since this paper was read, I have discovered a young specimen of this boa among the specimens from the Zoological Society, which they had received from Fernando Po. It is about half the length and diameter of the specimen from Old Calabar. It has the head shields more uniform, and as I supposed they might be when I described that specimen. It has three pairs of band-like frontal shields over the forehead, a rather large parietal shield behind them on the crown of the head, and two small subequal superciliary shields between the outer edge of the parietal and the eye, on each side a narrow transverse band-like central shield behind, and rather broader than the parietal shield, with a small scale-like shield, like those on the neck behind, and on the sides of it."

Although the above descriptions have thus already appeared in the proceedings of another Society, there has been no hesitation in fully quoting them, not perhaps because they ought rightfully to have first been given in the Proceedings of this Society, but that they are of sufficient interest to entitle them to repetition.

Of the other specimens of reptiles returned by Dr Gray, that labelled Ahatulla Chenonii will be found noticed in a most useful list prepared by him, at p. 161 of the above-mentioned part of the Zoological Society's Proceedings, No. 68 of the list, under the leading name of Ahætulla Irregularis, together with its synonyms; the localities assigned being Gambia, Fantee, and the Gold Coast. Another of the specimens will be found noticed in the same list, immediately following, under the name Ahætulla Smaragdina, together with its synonyms,

the localities assigned being Ashantee and Guinea. The next specimen, Causus Rhombeatus, will also be found in Dr Gray's list, p. 163, No. 86, with its synonyms (Hab. West Africa; Gold Coast, Liberia, South Africa); but it is more fully described in the catalogue of reptiles of the British Museum, 1844 (Snakes, p. 33). Of this snake the British Museum possesses four. The specimen named Boodon Geometricus will be found, with its synonyms, in Dr Gray's list, p. 159, No. 42, under the name Boadon Geometricus, Hab. West Africa; and the specimen named Onychocephalus Liberianus will be found with the single synonym Onychocephalus Liberiensis, under the name Onychopsis Liberiensis, in Dr Gray's list, p. 157, No. 18; Hab. Liberia, Calabar.

The last remaining specimen to be noticed is a lizard, Tiliqua Fernandii, described in the British Museum Catalogue (p. 110, Lizards) as Tiliqua Fernandi-the Fernando Po Tiliqua-of which an interesting account has already been given to this Society in a paper by Mr Andrew Murray, at p. 415 of the first volume of its Proceedings. The oblique cross brown bands along the brown sides should be bright scarlet or vermilion, but stuffed or preserved specimens seem to lose this brilliant colour, as it is not to be seen in the present specimen, although otherwise in excellent preservation.

V. On the Silicification of Organic Bodies. By ALEXANDER BRYSON, Esq., F.R.S.E.

The solution and deposition of silica has become a very important question, not only to the mineralogist, but to the physical geologist. Whilst the mineralogist has speculated on the forms of silicious minerals and fossils, he generally has arrived à priori at the conclusion that they were of aqueous origin; the geologist, on the other hand, has assumed them mostly as due to igneous action. M. Brogniart was the first to point out the true theory of the silicification in fossil woods, in an able paper published in the "Dictionnaire d'Histoire Naturelle." In 1828 Von Buch communicated a paper to the Academy of Sciences of Berlin, in which he boldly asserts that the silicifying process never immediately attacks the calcareous shell; that it develops itself only upon the organic sub

stance of the animal, or the organic matter contained in the shell, and that where such organic substance is not present there, no silicifying takes place. In support of these views of Von Buch, it may be remarked, that wherever shells are found embedded in a silicious matrix, they are generally entirely converted into silica, no doubt owing to the large quantity of animal matter contained in them before silicification took place. In no instance could I find a trace of calcareous matter remaining, clearly showing that either a chemical change had taken place, or a mechanical substitution of the silica for the whole calcareous matter.

In further proof of Von Buch's theory, I may quote a paper by Dr Bowerbank on a zoophyte (Alcyonites parasiticum) which he found enclosed in an agate. The interest attached to this paper is, that while we have no evidence of the time required for the silicification of calcareous bodies, and of woods and horny substances here, we have complete evidence of the rapidity of the change from the slight amount of the decomposition of so tender a zoophyte as an Alcyonium. On this point Dr Bowerbank remarks, "Nearly the whole of the animal within the agate is in a beautiful state of preservation, but there are a few spots which present evidence of the commencement of decomposition by the detachment of groups of cells from the mass of the polypidom; in these cases the remains of the tentacles, as might be expected, are very rarely to be seen, and the disrupted mass is totally without a sponge fibre. The envelopment of a tooth, or of hard calcareous bodies, such as shells, afford no definite information regarding the time necessary to accomplish such an operation. The investment even of such bodies as the rigid endurable horny fibres of that tribe of sponges which are usually to be observed embedded in flint, cherts, and moss agates gives also a considerable range of time to accomplish the fossilisation; but when we see such a soft and perishable substance as the fleshy body of the living Alcyonidae, and such delicate organs as the tentacula of the polypes thus preserved with such evident appearances of freshness and perfection, I own it excites in me the greatest astonishment that there should have been so rapid a deposit of silicious matter as must evidently have taken place