One of the characteristic features of the warmer and intertropical regions of the globe, is the presence in abundance of those highest forms of Crustacea, the Shore- and Land-crabs.

On the genus Necrosius.—This new genus is very near to Ozius, and is still more near to a small genus, established a few years since by M. Stimpson, named Spherozius. Like this last-named form, the carapace of Necrozius is remarkable for its globular form, its width scarcely surpassing its length. The curve of the buckler is slight in a transverse direction, but is great from back to front, the anterior border being much curved down. The latero-anterior borders are continuous, almost without interruption, with the latero-posterior, which latter are swollen. The frontal border (rostrum) projects a little, and is slightly depressed in the centre. The basal joint of the internal antennæ is large, and it is articulated obliquely beneath the front (rostrum). The basal joint of the external antennæ is short, not reaching to the front as in the Pseudozius of Dana, and in spherozius of Stimpson; the articulation is free and is not lodged in the internal obital cavity. With Ozius on the contrary, this basal joint is fully attached to the front.

A Week or two spent last month at Llandudno has given me the opportunity of examining the deposits on the Great Orme's Head, described by the Rev. T. G. Bonney in the August number of the Geological Magazine, and supposed by him to be the remains of a Kitchen Midden. The present communication is intended merely as a supplementary note to his paper. It appears that the beds, containing recent shells and bones, had been previously observed, and their true character ascertained, since the Rev. W. S. Symonds remarks, in some notes on the Geology of the district, “The beds of mussels and other shells on the Great Orme, which, at one time I imagined to have been elevated in raised beaches, Mr. Darbishire believes to be derived from old shell-heaps the accumulations of former inhabitants.”

The accompanying section shows the succession of beds from the Harlech grits, near the sixth milestone on the road from Dolgelly to Trawsfynydd, across their strike in a south-easterly direction, to the lower ash-bed of the Arenig group at the farm of Blaenau, five miles north-east from Dolgelly. In this section all the beds occur in regular sequence, although they are invaded by many intrusive masses and dykes of diabase; only the larger of which are shown in my section, as it would be impossible, on so small a scale to depict the innumerable protrusions of this rock that occur in the district. The section crosses, at Moel-Cors-y-garnedd, the southern flank of the mountain Rhobell-fawr, which is the largest mass of diabase in Wales. All along the eastern side of Rhobell-fawr the strata are completely inverted, as shown in diagram, so that the Festiniog beds (5 and 6) lie above the more recent Dolgelly beds (7 and 8), from underneath which the Tremadoc beds (9) come up, overlying the beds of slates and ashes belonging to the Arenig Group (10 and 11).

Since my former communication on this subject, which appeared in the Geological Magazine for April last, (p. 154) I have had several opportunities of re-visiting some of the cuttings, on the Midland Railway, therein referred to, respecting which some doubts were expressed in reference to the age of the deposits exposed to view, and, as they are now completed, more precise observations can be made than when they were only just commenced. The cutting, south-east from Westoning, (which, in an Editorial note, was suggested might be of Tertiary age) exposes a dark heavy clay, which, upon the most rigid examination, furnished not the least trace of rolled fragments of Chalk or flints, or any other substance so frequent in the Tertiary clays of this neighbourhood, which would lead to the inference that it had been deposited subsequently to the Cretaceous era. It, however, contains what would strongly indicate that it is coæval with the Greensand, namely, a continuous band of coprolitic nodules, averaging about a foot in thickness. This layer passes through about one-third of the cutting, and may be traced from its commencement on the north-west side of the hill, passing along the face of the cutting with a gentle dip, until it reaches the level of the line, when it passes out of sight, nor does it re-appear on the south-east side of the excavation. The fossils associated with the nodules are Lamna, Belemnites, Parasmilia, and Terebratulœ, all of which are abundant in the coprolite beds at Hexton and other places in the immediate vicinity. Both above and below the coprolites the caly is identical in character, and must have been deposited eontemporaneously with its associated nodules, and, as far as I can judge, it is the equivalent of the bed h of the section given by Mr. W. Whitaker, in the Quart. Journ. Geol. Soc., vol. xxi., 1865, pp. 399, “On the Chalk of Bucks.” About the middle of the cutting is a considerable accumulation of light-brown coloured drift-sands, that lie in a basin-like hollow, that has been eroded from the summit of the hill.

Having been for the last twelve months engaged in a careful study of the post-Tertiary geology of the eastern part of Shrop-shire, I have at length arrived at the conclusion that the denudation of the New Red Sandstone in this neighbourhood, and consequent excavation of the Tern basin, has been effected partly by glacial and partly by marine agency; the grounds upon which this conclusion is based being:—(1) An attentive consideration of the general form and outline of the basin; (2) A particular examination of the drift beds contained therein.