Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/677

Rh the name must consequently drop. The only statement made regarding it by Agassiz, is as follows:—

"Pygopterus Jamesoni, Agass. Sous ce nom j'ai distingué une seconde espèce de Burdiehouse, dont je ne connais encore que la mâchoire inférieure qui diffère de celle du P. mandibularis, en ce qu'elle est proportionnellement plus courte". As he does not, however, state how this jaw (the only relic found) differs from that of P. (Elonichthys) Bucklandi, I cannot help strongly suspecting that it belonged to the same fish.

The scale figured by Mr. T. P. Barkas, from the Northumberland coal-field, as belonging to a species of "Pygopterus" evidently appertains to the same fish as that from North Staffordshire, described by myself as Elonichthys semistriatus, as is also most probably the case with the mandible represented by him on the same plate.

III. Type of Pygopterus Greenockii, Agass. (genus Nematoptychius, Traquair).—Concerning "Pygopterus" Greenockii the following brief statement was made by Agassiz:—

"Espèce très-distincte sous le rapport spécifique, mais douteuse sous le rapport générique. Les fragmens connus ne sont guère que des têtes avec la partie antérieure du tronc. Les écailles qui recouvrent cette partie du corps sont plus hautes que longues, et diffèrent par-là de celles de tous les autres Pygopterus. Du terrain houiller de Newhaven. Il en existe plusieurs exemplaires dans la collection de Lord Greenock, qui sont tous contenus dans des géodes de fer hydraté carbonaté".

Although the original examples of this species, collected by Lord Greenock, and now in the Museum of the Royal Society of Edinburgh, were thus imperfect, there is hardly any Carboniferous fish concerning whose structure I have been able to acquire more complete information, my own collection being especially rich in its remains, and many other specimens being in the Edinburgh Museum of Science and Art. These specimens, some of them entire, confirm the doubts which Agassiz himself entertained regarding its generic position; and accordingly in 1875 I proposed for its reception the new genus Nematoptychius. The configuration of the scales is alone sufficient to demand its separation from Pygopterus. Those of the flanks are much higher than broad; their anterior covered margin is very narrow; the exposed surface is rhomboidal; but the acute angles are the anterior-inferior and posterior-superior; the articular spine is broad and triangular, and arises from the whole, or nearly the whole, of the narrow upper margin. The scales alter their form on the ventral aspect, where they become low and very small; their external ornament consists of fine, wavy, thread-like ridges. The pectorals are of moderate size, and have their principal