Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/670

570 referable to the same species—and to Dr. Hunter, of Braidwood, for the loan of a magnificent slab covered with its scales, bones, and fin-rays from the shale underlying the "Main Limestone" (Lower Limestone series) of that locality. All the specimens which have as yet been found have been fragmentary, consisting only of detached scales and bones, or of masses of scales either confused or adhering together to some extent in their original rows. Dr. Hunter's slab measures 20 inches in length by 11 in breadth. It displays, in the first place, a number of bones the forms of such of which as are determinable stamp the fish at once as a member of the family Palæoniscidæ. Among these may be recognized the median superethmoidal, which in this family forms the anterior projection of the snout over the mouth: and tying near it is the impression of a bone, 4 inches in length, which displays the characteristic form of the Palæoniscid maxillary. No impressions of teeth are seen; it is therefore unfortunate that the counterpart of the specimen could not be found, as the bony substance of the maxilla has evidently remained on it, the teeth not having been exposed. The lower portions of both clavicles are also seen; and the dimensions of these are such as to lead one to suppose that the length of each, when entire, could not have been less than five or six inches. The external ornamentation of all these bones is of a tubercular nature, the tubercles sometimes finer, sometimes coarser, occasionally showing a tendency towards a linear arrangement or to coalesce into short ridges.

Besides the numerous scattered scales which occur in the slab, there are two large patches in which the scales still cohere together in rows. One of these patches evidently represents a portion of the skin of the front of the flank, the position of the other being further back towards the caudal region. These flank-scales are large; one of the largest of them is $5⁄8$ inch in breadth; its exposed and ganoid area is nearly equilateral, measuring about $7⁄16$ inch in breadth and in height; this area is rhomboidal, but not acutely so, and is obliquely traversed by strong subparallel ridges, which proceed in a direction from above, downwards and backwards, occasionally branching and anastomosing, or, where two diverge, another being intercalated between, there being, on an average, five such ridges in the space of $1⁄8$ inch. The anterior covered area overlapped by the scale in front is extensive, being $3⁄16$ inch in breadth; its lower margin is more oblique than that of the sculptured portion, with which it consequently forms an obtuse angle; above it is produced into a prominent pointed process, where it coalesces with the narrower covered area of the upper margin, overlapped by the scale next above. From the middle of the upper margin there projects, in addition, the proper articular peg of the scale, stout and triangular in form. Near these scales are scattered others which were evidently situated towards the ventral aspect of the fore part of the fish. These display a similar sculpture of the exposed area; but their form is lower, narrower, and more oblique; the articular peg of the upper margin has disappeared; but the anterior superior pro-