gigantic ally, the Rhizodus of the Scottish Lower Carboniferous strata. I had previously observed the not uncommon occurrence of detached dentigerous bones belonging to R. Hibberti, which had exactly the same shape as the so-called præmaxillæ of Rhizodopsis, and, like them, frequently bear only one laniary, the large one in front. On now carefully examining the exterior of several more or less perfect mandibles, it became at once evident that the bone in question was nothing more or less than the dentary element, the rest of the outer surface of the jaw being formed by several additional bony plates quite analogous to those occurring also in Rhizodopsis. In Rhizodus there are four such additional plates: of these the posterior one, covering up the articular region, is probably equivalent to the angular element, though, indeed, occupying also the position of a supraangular; while in front of it, below the dentary, and forming the lower margin of the jaw, are three others, diminishing in size from behind forwards, and separated from each other by sutures passing obliquely forwards and upwards, and to which, as in Rhizodopsis, the name of infradentary may be applied.

Several detached specimens of the dentary bone of Rhizodus in the Edinburgh Museum exhibit its inner surface, which is also conformed just as in the corresponding element, the socalled præmaxilla, of Rhizodopsis. The upper margin, comparatively thin, is set with one row of small teeth; but at the symphysial extremity the bone shows a great thickening, the anterior part of which is marked by a very rough area for articulation with the bone of the opposite side. In this thickening is implanted the anterior great laniary, behind and close to which is another socket, usually empty, sometimes occupied by a "twin" tooth. There are also in the Museum several jaws seen from the internal aspect and in which the posterior laniaries are present; but being imbedded in hard ironstone, the surface of the bone is so injured as to render recognition of sutures a matter of difficulty: they show, however, very clearly that these posterior laniaries are implanted in a thickened ledge, somewhat nodulously enlarged round the base of each, and continuing backwards the symphysial thickening of the dentary proper-this ledge with its teeth being totally absent in the detached dentaries above alluded to. I now selected for special preparation two jaws, seen from the outer surface, and fortunately imbedded in a rather soft laminated clay. The first of

The more posteriorly situated laniaries of Rhizodus occur also occasionally double.

these was a portion of a comparatively small jaw, 34 inches in length, and broken across inch behind the stump of the second laniary; and by softening the matrix with water, I succeeded in completely detaching it and cleaning its inner surface. The surface of the bone being here quite intact, I obtained a clear proof of the fact which I had anticipated, viz. that the second laniary tooth is attached to a separate piece of bone articulated by a distinct suture to the anterior thickening. of the dentary, and having its outer surface in apposition with the flat inner surface of the dentary behind that thickening. The next jaw was a larger one, measuring 14 inches in length, showing three entire laniaries and the stump of a fourth, the articular extremity being, however, unfortunately broken off. Having covered up the outer surface of the specimen with a sufficient mass of Portland cement, I turned it over and worked down upon it from the other side, the preparation thus obtained entirely corroborating the conclusions previously arrived at. The large teeth are seen to be borne upon a thickened ledge, diminishing in strength from before backwards, the anterior part of which is the previously described symphysial thickening of the dentary proper, and carries the first great laniary; the suture between that and the anterior of the accessory internal dentary pieces bearing the second laniary is distinctly seen; but posteriorly the separation of the others is obscured by the obstinate adherence to the bone of a thin layer of the matrix, which cannot be thoroughly cleared off without injuring the surface. My attention was next directed to a block of the same laminated clay containing several bones of Rhizodus. From this I succeeded first in extracting the anterior half of an isolated dentary bone, that of the right side, showing the stump of the symphysial laniary with the adjoining empty socket. Then, lying about 2 inches from it in the same block, I observed a piece of bone bearing a large tooth, which, on being in like manner extracted entire, proved to be nothing more or less than the detached accessory piece carrying the second laniary of the same jaw, and would have fitted perfectly on to the dentary found beside it, had not the latter been a little distorted by crushing. Finally, several vertical sections through another mandible led to the very same result-namely, that the laniary teeth behind the great anterior one are attached to bone which is quite distinct from that of the dentary proper; and as the piece to which the second laniary is attached has occurred quite isolated, we may very safely assume that the third and fourth had also each a piece for themselves.

Summary.

The general results of the researches briefly detailed above may be summed up as follows.

The mandible has, as far as ascertained, essentially the same structure in Rhizodopsis as in Rhizodus. In both, the dentary element is narrow and pointed posteriorly, its upper margin bears one row of small teeth, while at the symphysis it is peculiarly thickened where it bears the first or anterior laniary. This bone, turned upside down, has, in Rhizodopsis, been previously considered to be the præmaxillary; the lastnamed element of the skull of that fish has now, however, been ascertained to be a different bone, which is quite similar in form and relations to the præmaxilla in other Crossopterygii.

The laniary teeth behind the anterior one are borne upon separate internal dentary ossicles, which, when the constituent elements of the lower jaw are broken up and separated, will also become disarticulated and dispersed. This is absolutely proved in Rhizodus, and may be considered morally certain in Rhizodopsis, though a clear view of the inner aspect of the complete mandible of the latter, with the posterior laniary teeth in situ, has not yet been obtained.

Below the dentary the inferior margin of the jaw is formed by a series of infradentary plates, while posteriorly the articular region is covered by a plate corresponding in position apparently both with the angular and supraangular elements. may add that, in one specimen of Rhizodopsis, I have seen very distinct evidence of a splenial.

I

The great complexity of the structure of the mandible in these forms and in the allied "Dendrodonts" of the Old Red Sandstone need not astonish us when we take into account the remarkably segmented splenial of the recent Amia, or the similarly segmented maxilla of Lepidosteus.

XXVI.-Description of a new Form of Ophiuridæ from New Zealand. By EDGAR A. SMITH, F.Z.S., Zoological Department, British Museum.

[Plate XV.]

THERE are three specimens of this very remarkable form of Ophiuridae in the British Museum-one presented by Major

Greenwood in 1850, and the two others by Captain Stokes, R.N., in 1855.

In general aspect it reminds one at once of the genus Ophiocoma, possessing a granular disk similar to that which obtains in that genus; and the characters of the arm-plates and of the true arm-spines are also congeneric; but the difference of the oral slits (rimæ) and the presence of two or more short flattened spines or scales which overlap one upon another and upon the uppermost true arm-spine, thus keeping them almost in a horizontal position, are characters which may be considered of sufficient importance to separate generically this curious species. The mouth-organs, namely the teeth proper, tooth-papillæ, and the jaws or framework which supports them, are exactly similar to those of the genus Ophiothrix; also the oral fissures are precisely like those of that genus-that is, are more in the form of wide holes than narrow slits as in Ophiocoma; and the first ambulacral tentacles are just within the rimæ and without scales. The side mouth-shields are likewise of the same character as in Ophiothrix, and are situated along the lower margins of the oral shields, as is almost invariably the case in that genus. However, the granular disk not showing radial shields, and the, presence of mouth-papillæ, are differences which easily dissociate the present genus from it.

OPHIOPTERIS , gen. nov.

Disk covered with a granulous skin as in Ophiocoma; teeth, tooth-papillæ, oral and adoral shields, and the mouthfissures as in Ophiothrix; oral papilla present; brachial shields and true spines similar to Ophiocoma; the arms provided with 2-3 compressed imbricating scales or compressed spines above the uppermost spines; two genital slits; ambulacral scales present.

Ophiopteris antipodum, sp. nov.

Disk roundly subpentagonal, somewhat lobed between the rays, closely and coarsely granulated on the dorsal surface, and beneath on the interbrachial spaces covered with crowded short spines; rays 4-5 times as long as the diameter of the disk; oral shields small, somewhat heart-shaped, with a slight point both on the inner and aboral sides; madreporic shield distinct, larger than the others, and lobed a little on each side; side

opis a snake and Tтéρis a fern. The rays call to mind the appearance of certain kinds of ferns.

mouth-shields irregular, narrow, lying along the lower margins of the orals, and not quite meeting within; mouthpapillæ about six to each mouth-angle, three on each side, small, not at all conspicuous; tooth-papillæ very numerous, arranged in six vertical rows above, gradually diminishing until there are but two series where they meet the teeth; they extend far within the mouth, so that the teeth are not visible; the papillæ of the outer rows are a trifle longer than the intermediate ones, and increase in size as they approach. the teeth, and those at the upper end of the tooth-column are very small and irregularly clustering. Teeth 5, subequal, roundly truncated at the ends and thicker in the middle than at their lateral edges.

Lower arm-plates at the border of the disk about twice as broad as long, gradually becoming proportionally longer as the end of the arm is approached; their form is irregularly heptagonal, the two sides towards the mouth sloping to a slight point; on the aboral side they are faintly excavated in the middle, and arcuately sloping on each side of this slight sinus towards the lateral margins, which are also concave; upper arm-plates remarkably flat, twice as broad as long, and gradually, like the lower ones, becoming proportionally longer towards the end of the ray; in form they are transversely oblong, sharply pointed on each side, the points fitting in between the very narrow lateral plates; the latter just meet below between the lower arm-plates, but not quite above; arm-spines in four series (near the disk sometimes five), the lowest the shortest, the uppermost but one the longest, and the other two about equal in length, but the uppermost one the stoutest; all the spines are rather flattened, not acutely pointed, and much compressed at the tips and truncated. Above the base of each spine of the uppermost series are two (here and there three) short, broad, compressed spines or scales one upon another, the one nearest the lateral spine the largest and about a fourth its length; one tentacle-scale, small, roundish ; genital slits two in each interbrachial space, extending from the margin of the disks to the oral shields.

The colour above is uniformly dull brown, and beneath the rays and ray-spines rather paler. The interbrachial spaces below are dark like the dorsal surface.

Diameter of the disk about 26 millims.; width of upper arm-plates 3, of lower ones 23; length of longest spine 51. Remarks. The form of the mouth-shields is subject to considerable variation. In the largest specimen they are almost as long as broad, whilst in a smaller one they are much broader than long.