PAL^EONISCUS, GYROLEP1S, AND PYGOPTERUS. 575 



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. ffumboldtii, Ag., P. mandibidaris, Ag., and 

 P. latus, Egerton, — P. sadptus, Ag., being pretty certainly, as sug- 

 gested by Sir Philip Grey-Egerton, only a synonym of P. mandibu- 

 laris *, Agassiz not having been aware that the anterior scales of 

 this species were sculptured with diagonal striae. The nearest 

 ajjproach to Pygopterus in general form is made by some of the much 

 smaller Carboniferous fishes which I include in the genus Bhadi- 

 nichtliys ; 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 " echancree," is not prolonged 

 backwards in the same manner. In the structure of the pectoral 

 fin it also resembles Oxygnathus and Thrissonotus, as well as Bhadi- 

 nkhthys : in Thrissonotus, also, the anal fin has apparently a some- 

 what similar formf . 



II. Type of P. BucJclandi, 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 £, 

 cannot now be found. A figure of it, however, is given by Hibbert, 

 in his celebrated memoir on the Burdiehouse Limestone §, from which 

 figure, along with the very brief notice of this species in the ' Pois- 

 sons Eossiles,' I feel pretty confident in referring to it a number of 

 mostly fragmentary remains of a large Palgeoniscoid fish from Bur- 

 diehouse, contained in the Edinburgh Museum of Science and Art. 

 All that Agassiz says of it is as follows : — 



" Pygopterus BucJclandi, Agassiz. Espece caracterise par la 

 petitesse et la forme allongee de ses ecailles, et par son anale tres- 

 rapprochee de la caudale. Elle est a peu pres de la taille du P. 

 mandibularis et provient du calcaire de Burdiehouse en Ecosse "j|. 



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. 



t Dec. Geol. Snrv. ix. 1858, pi. 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 men- 

 tioned by Agassiz as belonging to the Royal Society of Edinburgh are in their 

 places. 



§ Trans. Roy. Soc. Edinb. vol. xiii. pi. 7. fig. 2. 



|| ' Poissons Fossiles,' vol. ii. pt. 2, p. 77. 



