(One half nat. size.)] That suite of shoulder-bones that in the osseous fishes forms the belt or frame on which the opercules rest, and furnishes the base of the pectorals, was represented in the _Asterolepis_, as in the sturgeon, by a ring of strong osseous plates, which, in one of the two species of which trace is to be found among the rocks of Thurso, were curiously fretted on their external surfaces, and in the other species comparatively smooth. The largest, or coracoidian plate of the ring, as it occurs in the more ornate species, (fig. 38,) might be readily enough mistaken, when seen with only its surface exposed for the ichthyodorulite of some large fish, allied, mayhap, to the _Gyracanthus formosus_ of the Coal Measures; but when detached from the stone, the hollow form and peculiar striæ of the inferior surface serve to establish its true character as a dermal plate. The diagonal furrowings which traversed it, as the twisted flutings traverse a Gothic column moulded after the type of the Apprentice Pillar in Roslin chapel, seem to have underlaid the edge of the opercule; at least I find a similar arrangement in the shoulder-plates of a large species of _Diplopterus_, which are deeply grooved and furrowed where the opercule rested, as if with the design of keeping up a communication between the branchiæ and the external element, even when the gill-cover was pressed closely down upon them. And,—as in these shoulder-plates of the _Diplopterus_ the furrows yield their place beyond the edge of the opercule to the punctulated enamel common to the outer surface of all the creature’s external plates and scales,—we find them yielding their place, in the shoulder-plates of the _Asterolepis_, to the starred tubercles. [Illustration: Fig. 38. SHOULDER (_i. e._ CORACOID?) PLATE OF ASTEROLEPIS. (One third nat. size, linear.)] [Illustration: Fig. 39. DERMAL BONES OF ASTEROLEPIS. (One third nat. size, linear.)] [Illustration: Fig. 40. INTERNAL BONES OF ASTEROLEPIS. (One half nat. size, linear.)]