PAL.EONISCUS, GYROLEPIS, AND PYGOPTERUS. 571 



duction of the covered areas is proportionally longer and more acute. 

 The scales of the other coherent patch are smaller in size, and more 

 obliquely rhomboidal in form, as regards the exposed surface ; they 

 are further distinguished by the absence of the articular peg of the 

 upper margin, and by the much greater narrowness of the covered 

 areas, which are not specially produced upwards and forwards. 

 Their thickness is also very considerable, being no less than ^ inch 

 in one of these scales entirely detached from the matrix, and 

 measuring about ^ inch in breadth. A difference is also observable 

 in the sculpture of these posterior scales, viz. a tendency of the 

 ridges to coalesce in a reticulating manner towards the posterior, 

 superior, and interior-inferior obtuse angles of the scale, so as to 

 interrupt the intervening furrows in these two regions, converting 

 them more or less into pits. 



The specimen also exhibits, as already mentioned, many detached 

 and broken-up, transversely jointed fin-rays, some of which attain a 

 breadth of ^ inch ; the length of their joints is somewhat less, but 

 varies in different rays. These rays are all seen only from their 

 internal non-ganoid surfaces. 



As already stated, it is quite evident that the fish to which these 

 remains belonged is a member of the family Palaeoniscidse ; and the 

 form and thickness of the scales, with their very large anterior 

 covered area, and the nature of their sculpture, along with the 

 peculiar tubercular ornamentation of the cephalic and shoulder- 

 bones, point out, as it seems to me, that Acrolepis is the genus to 

 which it should be referred. The scales of the Permian A. Sedg- 

 ivickii are quite similar in shape, though proportionally smaller and 

 with fewer ridges. The tendency to reticulation of the ridges on 

 certain parts of the posterior scales of the Lanarkshire fish reminds 

 us also of the peculiar sculpture which is characteristic of the entire 

 scale and over the whole body of A. exsculptus. The narrow ventral 

 scales are, indeed, undistinguishable from the one from the Carboni- 

 ferous Limestone of Derbyshire contained in the Cambridge Museum, 

 and figured by M c Coy as Acrolepis Hopkinsii *; but if that be the 

 same, as I believe it to be, with a fish from the Millstone Grit of 

 Hebden Bridge, of which several beautiful fragments are in the 

 collection of Mr. John Aitken of Bacup, it is a distinct species, and 

 differs from A. Rankinei in other respects. 



In conclusion, if all definition of Gyrolepis as a genus is at pre- 

 sent impossible, if the diagonal ridged scale-ornament, supposed to 

 be characteristic of it, is also characteristic of the scales of many 

 species belonging to various other genera, such as Acrolepis, Elo- 

 nichthys, Rliabdolepis, Cosmoptychius, &c, and if the " Gyrolepis " 

 Rankinei of Agassiz be referable to Acrolepis, then there is, as I 

 have maintained above, no longer any justification for the retention 

 of the name " Gyrolepis " in our lists of British Carboniferous 

 fossils. 



* 'British Palaeozoic Rocks and Fossils,' p. 609, pi. 'Sy. fig. 10. 



