and Systematic Position o/" Cheirolepis. 241 



one from above downwards and forwards — exactly the oppo- 

 site ; and this change takes phice nearly opposite the middle 

 of the origin of the lower lobe of the caudal. Though this 

 fact is not alluded to by Pander in his description, it is most 

 distinctly represented in tab. ix. fig. 1 of liis illustrations. 

 On examining the tail oi Falceoniscics, Ambli/ptencs, or any 

 allied genera, precisely the same phenomenon is invariably 

 seen to occur — viz. the sudden alteration of the direction of 

 the oblique bands of scales on tiie upper caudal lobe to one 

 at right angles to that of the bands covering the rest of the 

 body*. In Cheirolepis, too, as in these genera, the scales 

 clothing the sides of this caudal body-prolongation become 

 acutely lozenge-shaped as we trace them on towards the tip 

 of the tail. 1 have not observed in front of the azygos fins 

 the peculiar large scales which in most Pala^oniscidaj precede 

 the dorsal, anal, and lower lobe of the caudal, ultimately 

 passing into the fulcra of these fins ; but on the upper margin 

 of the tail the arrano-cment of large V-scales is characteristic, 

 and entirely in accordance with that in the heterocercal Lepi- 

 dosteids and also in Acipenser and Polyodon. These have 

 been so well illustrated in one of Prof. M'Coy's figures f that 

 there is no necessity for describing them fui'ther in this place ; 

 enough has been said to show how strikingly Cheirolepis 

 deviates from the Acanthodidte in all points connected with 

 the scales save their minute size, and how close, on the other 

 hand, is the approach which it makes to Falceoniscus in the 

 general arrangement of these appendages. And even as 

 regards the smallness of the scales, it is to some extent ke])t 

 in countenajice by the undoubtedly Palteoniscoid Myriolepifi 

 Clarkei, Egerton, so far as we can judge from the beautiful 

 figure given by its eminent describer|. 



The fins of Cheirolepis are composed of very numerous rays 

 frequently dichotomizing, and divided transversely by very 

 numerous articulations ; the rays are very closely set, and the 

 demi-rays of each side imbricate over each other from before 

 backwards, like those of the anal fin of Polypterus, while 

 conspicuous fulcral scales seiTate their anterior margins. The 

 arrangement here is in all essential respects identical with 



* It is an interesting fact that the patch of rhombic scales on the side 

 of the vertebral prolongation in the tail of Acipmiser and of Poli/odon 

 (in the latter genus the only scales, along with the "fulcra " above them, 

 which occur on the body at all) coiTespond exactly in aiTangement with 

 this peculiarly arranged caudal patch of scales in the Palaeoniscidae. A 

 similar arrangement is also traceable in the imperfectly heterocercal tail 

 of Lepidostetis. 



t ' I'alajozoic Fossils," pi. 2 d. fig. •'}. 



I Quart. Joui-n. Geol. Soc. xx. I8G3, pi. i. fig. 1. 



