Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/496

 in making it the type of a new genus, Mesodon, to which must be added Gyrodus gibbosus, Munster, and Pycnodus liassicus, described by myself in the 8th Decade of the 'Memoirs of the Geological Survey,' plate x. On comparing the Scotch specimen with the other species of Gyrodus of which the characters of the scales are known, I find it differs from them all ; I have therefore ventured to give it a specific name, although it is impossible to affirm it to be a new species until more is known of the many species of the genus which have been named from the teeth alone. The scales in this specimen are very large, and have a dense lustrous surface of ganoine. Some of these, on the flanks, measure above an inch in length, including the processes. The lateral line traverses the several series of scales below the column ; the scales above this line decrease in size to the dorsal ridge-scales, while below it they increase nearly to the ventral border. The scales in the hinder part of the body are considerably smaller than those in front ; but they retain the characteristic surface-ornament throughout. This consists of an elaborate pattern in relief, composed of vermicular fillets interspersed with granules, which covers the whole exposed portion of the scales. At the two extremities of the trunk the granules preponderate over the labyrinthic pattern. The nearest approach to this scale-armature is found in a gigantic specimen from Solenhofen, in the Munich Museum, called Gyrodus rhomboidalis ; but there are strongly marked differences between this and the Scotch species.

Fig. 1. — Tooth of Gyrodus Fig. 2. — Scale of Gyrodus Goweri. Goweri.

Mr. Joass is unable to point out the particular bed from which this specimen is derived, but he says it was apparently beneath the siliceous sandstone of Braambury Hill, and decidedly above the calcareous grits, clays, and shales of Dunrobin. On referring to Sir Roderick Murchison's paper on the " Coalfield of Brora " *, I find the beds exposed on the coast between Culgower and Portgower are considered to belong to the middle portion of the Oolitic series,


 * Trans. Geol. Soc. 2nd series, vol. ii. pl. xxxi.