/. — Pleuracanthidce. 707 



o£ a single piece, which towards its hinder part is bent on its outer edge in the 

 form of a knee. This edge supports a number of fin-rays, the anterior ones fine 

 and short, those behind longer and thicker. From the knee-shaped angle 

 springs a strong distinctly jointed ray (axis of archipterygium). To this are 

 attached, on its outer margin, seventeen thick strong rays ; and on its inner 

 margin a number of smaller and closer rays. In the Euppersdorf specimen 

 it is not clear by what means the knee-shaped bone was attached at its proximal 

 extremity. The ventral fins are similarly connected to those of the pectoral. A 

 broad, short geniculate bone was suspended from the vertebral column, and to 

 this was attached an articulated primary ray as in the pectoral fin ; but they 

 differ from the pectorals in having lateral rays only on the outer margin. 



M. Beyrich described and discussed, a year later, the relationship of a 

 fish * similar in all essential respects to the Orthacanthus described by Goldfuss, 

 except that in this specimen the spine was flattened before and behind, and 

 had on each side rows of sharp, short, hook-shaped, backward-pointing teeth. 

 To this fish the new generic name Xenacanthus was given, and the opinion 

 expressed that Orthacanthus Dechenii of Goldfuss must be given up in its favour ; 

 and further that though the spine is evidently the same genus as the Fleuracanthus 

 of Agassiz, which has priority, the latter is only known as the name of a spine, and 

 consequently must give way to Xenacanthus, which represents a more or less 

 perfect fish. 



Sir Philip de Malpas Grey Egerton, at the meeting of the British Association 

 at Glasgow, in the year 1855, drew attention to the generic identity of the spines 

 called Fleuracanthus and Xenacanthus, and the teeth named Diplodus ; and in 

 1857t he published a paper in the " Annals and Magazine of Natural History," in 

 which the claim of Fleuracanthus to priority over the other names is enforced, and 

 consequently it should stand as the name of the genus. 



It was suggested by Prof. li. B. Geinitz that the ventral plates might have 

 been a sucker, and the fish allied to the genus Cyclopterus.X 



In 1867, Prof. D. Rudolph Kner published a memoir, " Ueber Orthacanthus 

 Decheni, Goldf. oder Xenacanthus Decheni Beyr."§ Specimens located in the 

 museums of Dresden, Berlin, Breslau, Vienna, and others are described in detail. 

 Kner argues that the two genera named, along with Diplodus teeth, are identical, 

 as was stated by Goldfuss twenty years previously. The fish is described as 

 having a large head, somewhat flat, with a large rounded terminal mouth. The 

 pectoral fins were broadly expanded and the body tapered towards the tail. The 



* Bericlit der Konigl. Preussischen Akademie der Wissenscliaften, p. 24, 1848. 



t Ann. Mag. Nat. Hist., ser. 2, vol. xx., p. 423. 



J Der Dyas, p. 23, pi. xxin., fig. 1, 1861. 



§ Sitzungsberichte Kaiser. Akad. Wiss. "Wien, vol. Iv., pt. i., p. 540, pis. i.-x. 1867. 



