country (where the old rocks were chiefly composed of Carboniferous Limestone), the prevalence of arenaceous deposits at the base of the Trias fringing the north-east and south slopes of the Devonian grits and shales of the Quantocks, the basement breccias and sands of the West Somerset and South Devon Trias (where the older rocks chiefly consist of Culmiferous and Devonian shales and grits), and the admixture of calcareous material in the form of derived fragments or in the matrix in places where neighbouring exposures of limestone were favourable for their production; so that we are not only unable to see any reason why the Muschelkalk should present similar characteristics in different areas, but fail to see why its representative should form a perfectly distinct division.

Whether the Budleigh pebbles travelled from Normandy or Cornwall, their advent seems to mark an epoch in the Triassic history of Devon, when either by the breaking of a barrier, allowing the incursion of foreign sediments into a salt lake or inland sea, or by a natural extension of the local sources of derivation, a supply of foreign material was swept into the area, furnishing the depositing agents with a different supply from that which had before been and was afterwards afforded by the local rocks.

In the Geological-Survey memoir on this area the bibliography of the subject will be gone into, and these few precursory notes will be modified and strengthened, when additional observations, greater latitude, and time allow us to enter into details and amplify many in our possession not alluded to here*.

DISCUSSION.

Mr. ETHERIDGE remarked that the Rhætics form a most important feature in Somersetshire. He thought that the ignorance of the Triassic rocks so common among geologists was to be ascribed to a great extent to the want of interest attaching to these nonfossiliferous red beds; and hence our thanks were due to those who, like Mr. Ussher, would work upon them.

Prof. RAMSAY said that Sir Henry De la Beche grouped the whole of the Triassic rocks together, but nevertheless there was no doubt that he fully understood their nature. In passing over part of the country, he had once fancied that some of the lower breccias might be Permian; but he had never been able to investigate the matter.

The AUTHOR remarked that if the Lower Breccias were Permian, the Bunter and Muschelkalk must be also represented, in the absence of unconformity.

Should any of my observations tally with those of my predecessors in the field, I have only to state that the latter part of this epitome has in a still more abstracted form appeared in the Geological Magazine,' dec. 2, vol. ii. No. 4, April 1875, and has been strung together and condensed entirely from my own notes and observations.

41. On the DISCOVERY of MELONITES in BRITAIN. BY WALTER KEEPING, Esq., B.A., of the Woodwardian Museum, Scholar of Christ's College, Cambridge. (Read March 22, 1876.)

(Communicated by Professor Hughes.)

In the appendix to a paper read before the Geological Society, June 9, 1875, I noticed the discovery of a large Urchin, nearly allied to the American genus Melonites, from the Carboniferous Limestone of Derbyshire, and preserved in the museum of the Geological Survey. I have since been permitted to examine the specimen more carefully, so as to determine it to be a new species of Melonites, a type of Echinoids characterized by its numerous ranges of ambulacral plates, which until now was unknown beyond the boundaries of the New World.

Another fragment, smaller, but well preserved and presenting all the characteristics of the species, may be seen in the British Museum. Description of the specimens.-The larger specimen is a confused mass of stout plates covering an area of 7 inches by 7 inches. Among these may be seen some broad bands and broken masses of another set of plates, which are each perforated by a pair of pores. From the arrangement of this latter system of plates, converging, as they do, roughly to the centre of the specimen, we see that this is the remains of one large Echinoid broken up and much disarranged, the larger scattered plates having formed its interambulacral areas, the masses of smaller plates its ambulacral zones.

The interambulacral plates (figs. 3, 4) are very numerous, and are all about the same size, which shows that new series of plates were intercalated to form the increasing circumference towards the equator of the test, where there must have been as many as eight or nine* ranges of plates. The plates themselves are very thick, and are rather irregular in form, most of them being unequally six-sided; others are pentagonal, with one face rounded. These latter formed the marginal ranges of plates, and they are marked with indentations for the ambulacral plates, with which they articulated. The surfaces of all are ornamented with closely set minute tubercles.

The plates were articulated with each other in a very irregular manner, some of their edges being perpendicular to the surface, while others are inclined as much as 30°, every intermediate stage being seen. The marginal ranges share the irregularity so characteristic of this Urchin; for some of these plates are bevelled off from their upper edges, others from the lower, so that in some parts of the test the ambulacral areas overlapped the interambulacrals, in others vice versa.

The ambulacral areas are in better condition. When the test was crushed their plates still cohered, and the areas were broken up into

*Supposing, as the specimen seems to indicate, that the circumference of the test was that of a circle with 34 inches radius, then, the ambulacral areas being 36 millims. broad (see infrà), the interambulacral areas were 72 millims. broad; and allowing each interambulacral plate 8 millims., there were nine ranges of such plates at the ambitus.

masses of various shapes, the larger ones remaining as broad bands converging to the centre. Their upper surface is distinctly convex both longitudinally and laterally; on one border they are festooned to receive the convex articulations of the adjoining interambulacral plates; but the opposite edge is a regular simply denticulated border (w, fig. 1). I therefore believe that these masses are broken halves only of the ambulacral areas-the festooned edge being the outer border of the area and the denticulated edge its middle line. An examination of the constituent plates confirms this view; for the pores which they bear are all situated towards that edge of the plate which is nearest the festooned border.

We have seen that each half of an ambulacral area is convex laterally; they are in fact much more convex than the general surface of a test 7 inches in diameter could have been; and they must therefore have stood out as ten broad ribs on the test, set in pairs separated by a gentle valley in the median part of the ambulacral areas, and by the broader planes of the interambulacral areas.

The half ambulacral areas, as here preserved (see fig. 2), are composed of six or seven ranges of small irregular plates, which are broader than high, thicker than broad, and ornamented with minute tubercles like the interambulacral plates. The middle ranges are more regular. Each plate is perforated by a pair of pores, subtriangular where best preserved, and situated close to that edge of the plate which is nearest the festooned border. Although the plates are so irregular, yet the pores are most of them arranged in lines and set in shallow grooves running longitudinally upon the areas. On the internal surface of the test these grooves (or "poriferous furrows," as they may be called) are represented by a corresponding set of ridges.

The tubercles form a very uniform granulation over the whole test, but are best marked on the ambulacral areas. They are imperforate, without boss, and are of two orders: the larger ones, which are most numerous, are surrounded by a smooth areola, bounded by an elevated ring (fig. 5); contiguous rings are almost in contact.

On the surface of one of the ambulacral masses and elsewhere on the block some minute acicular spines are abundantly scattered; the microscope shows them to be sulcated, with a prominent collar at the base (fig. 6).

The dimensions of the specimen are as follows, viz. :—

Figs. 1-6.-Melonites Etheridgii, sp. n., from the Carboniferous Limestone of Derbyshire.

Fig. 1. Crushed specimen of Melonites Etheridgii, n. sp., half nat. size (Museum of Practical Geology).

Fig. 2. The ambulacral mass marked x in fig. 1. The outer festooned border

and the spines are shown.

Fig. 3. An interambulacral plate, showing the bevelled edge and the tubercles. Fig. 4. One of the marginal interambulacral plates, showing the grooves for the articulation of the ambulacral plates.

Fig. 5. Tubercles, magnified. N.B. The rings around the tubercles are here made to look too angular and too prominent.

Fig. 6. Spine, much magnified.

The British-Museum specimen is smaller (4 inches by 3 inches); but it is a fragment of probably quite as large an individual, as we see from the size of its plates.

On one side the test has been much disturbed, the whole surface being covered with a confused mass of interambulacral plates and a few ambulacrals; but on the other surface we have a well-preserved interambulacral area composed of five or six ranges of plates, an extra range being intercalated between the others as we approach the equator. The outer edges of the bordering ranges are bevelled off, showing that they were overlapped by the ambulacral plates; these latter are seen confusedly heaped together in two masses bordering the interambulacral area on either side.

The tubercles and spines are well preserved.

It is remarkable that whereas in the larger specimen the ambulacral areas are preserved with their plates in position amid the scattered plates of the interambulacral system, here it is the ambulacral ranges that have given way, while the interambulacrals still preserve their natural relations.

MELONITES ETHERIDGII, n. sp.

Specific Characters.-Test large (diameter of crushed specimen 7 inches), spheroidal (?), composed of very thick plates arranged in five ambulacral and five interambulacral areas. All the plates ornamented with minute tubercles for the support of the spines.

Interambulacral areas broader than (twice as broad as?) the ambulacrals, composed of numerous (nine?) ranges of plates, marginal ranges pentagonal, the rest hexagonal, articulating with each other by faces which vary from a right angle to one of thirty degrees with the exposed surface. Ambulacral areas large (14 inch wide), each consisting of two broad ribs separated by a slight depression along its median line running from mouth to anus; composed of numerous (twelve to fourteen) ranges of irregular plates, each perforated by a pair of simple pores on its outer margin.

Tubercles minute, imperforate, without boss, of two orders, the larger kind surrounded by a smooth areola, bounded by an elevated ring.

Spines small (length 3-6 millims.), tapering, coarsely sulcate, with a prominent collar round the articular end.

Affinities and Differences.-The only forms which require a close comparison with our fossil belong to the genera Melonites and Oligoporus of the group Perischoechinidae; with these it agrees in the thickness of its test, its numerous ambulacral and interambulacral plates, and in the absence of large tubercles; but Oligoporus has not more than four ranges of plates in its ambulacral areas.

As a species, this is well distinguished from Melonites multiporus, N. & O., by the characters of its ambulacral areas: these are composed of twelve or fourteen ranges of plates separated into two zones by a median depression, and the two middle ranges are not larger than the others; in M. multiporus, N. & O., they are composed of eight