To this type, which has as yet occurred only in rocks of Permian age, the term Pygopterus ought in future to be strictly limited. Here are embraced P. Humboldtii, Ag., P. mandibularis, Ag., and P. latus, Egerton,—P. sculptus, Ag., being pretty certainly, as suggested by Sir Philip Grey-Egerton, only a synonym of P. mandibularis[1], Agassiz not having been aware that the anterior scales of this species were sculptured with diagonal striæ. The nearest approach to Pygopterus in general form is made by some of the much smaller Carboniferous fishes which I include in the genus Rhadinichthys; but in all of these the scales are proportionally larger and thicker, the caudal body-prolongation is not so powerfully developed, and the anal fin, though considerably "échancrée," is not prolonged backwards in the same manner. In the structure of the pectoral fin it also resembles Oxygnathus and Thrissonotus, as well as Rhadinichthys: in Thrissonotus, also, the anal fin has apparently a somewhat similar form[2].
II. Type of P. Bucklandi, Ag. (genus Elonichthys, Giebel). This species has never been described; and the original type, stated by Agassiz to be in the Museum of the Royal Society of Edinburgh[3], cannot now be found. A figure of it, however, is given by Hibbert, in his celebrated memoir on the Burdiehouse Limestone[4], from which figure, along with the very brief notice of this species in the 'Poissons Fossiles,' I feel pretty confident in referring to it a number of mostly fragmentary remains of a large Palæoniscoid fish from Burdiehouse, contained in the Edinburgh Museum of Science and Art. All that Agassiz says of it is as follows:—
"Pygopterus Bucklandi, Agassiz. Espèce caractérisé par la petitesse et la forme allongée de ses écailles, et par son anale très-rapprochée de la caudale. Elle est à peu près de la taille du P. mandibularis et provient du calcaire de Burdiehouse en Ecosse"[5].
Hibbert's figure represents only the posterior half of the fish, with the dorsal, anal, and caudal fins; and the two former strike one at the first glance as having the position and shape, not of those in Pygopterus but in Elonichthys. In fact, the approximation of the anal to the caudal, mentioned by Agassiz as a specific mark, is in reality a generic one; moreover, not being prolonged backwards, the anal resembles the dorsal in size and shape, while the latter is placed relatively further forwards. A comparison of this figure with the actual specimens to which I have referred, shows that we have here to deal with a fish which is certainly not a Pygopterus, but a species closely allied to those from the North-Staffordshire Coal-field, which I have recently described as Elonichthys semistriatus, E. caudalis, and E. oblongus, as well as to the E. striolatus, which
- ↑ In King's 'Permian Fossils,' p. 233.
- ↑ Dec. Geol. Surv. ix. 1858, pl. 2.
- ↑ It is possible that this is a mistake, and that the specimen may have been in the private collection of Dr. Hibbert, as all the other type specimens mentioned by Agassiz as belonging to the Royal Society of Edinburgh are in their places.
- ↑ Trans. Roy. Soc. Edinb. vol. xiii. pl. 7. fig. 2.
- ↑ 'Poissons Fossiles,' vol. ii. pt. 2, p. 77.
