﻿STRUCTURE OP THE PAL^ONISCID^E. 



29 



Scales of the Body. 



The scales in the Palaonisckla are osseous, sometimes pretty thick ; their form is rhom- 

 boidal. 1 They are arranged (PI. I, fig. 1, PI. II, fig. 1) in oblique or slightly sigmoid dorso- 

 ventral rows or bands, which above and below meet their fellows of the opposite side in a 

 V-like manner, the point of the V being directed forwards on the dorsal, backwards on the 

 ventral median line. The scales forming these bands fall also into longitudinal or lateral 

 series, and in these the upper margin of each scale terminates posteriorly, as seen in the 

 exterior of the body, a little above that of the scale immediately behind. The direction 

 of the dorso-ventral bands of scales continues with slightly increasing obliquity to nearly 

 opposite the bifurcation of the caudal fin, where the tail-pedicle terminates below and behind 

 in a rounded contour opposite the origin of the lower lobe, being, however, above and 

 behind continued into that narrow prolongation of the body-axis which passes along the 

 upper lobe of the fin. Here opposite the lower caudal lobe a sudden change in the 

 arrangement of the scales takes place, those on the sides of the prolongation of the body- 

 axis being now arranged in very oblique rows which proceed downwards and forwards, 

 or upwards and backwards, terminating in the acute and imbricating V-shaped scales 

 which run along the upper margin, and through whose intervention they are connected 

 with the corresponding bands of the opposite side. It is interesting to observe that this 

 arrangement corresponds exactly with that of the scales on the caudal prolongation of the 

 body-axis in the living Acipenseroids, and which in Polyodon (PI. VII, fig. 3) are the 

 only scales left on the body ; a remnant of the same arrangement is also seen in the 

 semiheterocercal tail of the recent Lejndosteus and its Mesozoic allies. Before the change 

 takes place, the last or the two last of the ordinary dorso-ventral bands may very 

 commonly be seen to bifurcate about half way down towards the caudal fin. 



If we now take as an example one of the flank scales in Palaoniscus, and in the 

 majority of the other genera they are very similarly conformed, the shape is rhomboidal, 

 the upper margin is slightly concave, the lower correspondingly convex ; the anterior and 

 posterior margins are straight, the posterior being finely serrated, though that is in some 

 oases plain. The outer surface shows a narrow area along the anterior margin overlapped 

 by the scale in front, this area being very narrow in some genera {Elonichthys, &c), in 

 others rather extensive {Acrolepis). The upper margin is likewise slightly bevelled 

 off to allow of the overlapping of the scale next above. The free surface is ganoid and 

 brilliantly polished, and may be quite smooth or, as is more commonly the case, variously 



1 Professor A. Fric, of Prague, has recently discovered in the uppermost Carboniferous rocks of 

 Bohemia a new genus of fishes, " die, bei dem Gesammthabitus eines Palseoniscus, mit Cycloiden- 

 Schuppen versehen ist" ('Sitzungsb. der k. bohm. Gesellscb. der Wissenschaften,' Marz, 1875). This 

 most interesting form has not yet been named or fully described ; palaeontologists will, therefore, look 

 forward with much interest to the promised publication in full of Professor Frio's researches into the 

 vertebrate fauna of the coal-basin of Pilsen and Rakonitz. 



