578 R. H. TRAQUAIR ON AMBLYPTERUS, PAL^ONISCTTS, ETC. 



rays unarticulated only for about i of their length ; the dorsal and 

 anal fins are large and triangular, the dorsal being placed far back 

 and nearly opposite the anal. The latter is slightly larger than the 

 dorsal, but is similar to it in shape, and is not prolonged backwards 

 in the fringe-like maimer characteristic of Pygopterus. 



For further details regarding the structure of this genus I must 

 refer to my previous papers on the subject *. A second species, 

 which I have named N. gracilis, has also recently turned up in the 

 black-band ironstone (Carboniferous Limestone series) of Gilmerton, 

 near Edinburgh f. 



It thus follows that there is no Carboniferous species of Pygopterus 

 as yet known, and that it must consequently be regarded as strictly 

 a Permian genus, though in this case, as in others, negative evidence 

 may be at any time overturned. I have also, in the preceding 

 pages, endeavoured to show that a better understanding of the Car- 

 boniferous species hitherto ascribed to A mblypterus, Palctioniseus, and 

 Gyrolejois excludes these genera also from the Carboniferous list, as 

 far as our present knowledge goes. This is especially important 

 with regard to the questions still pending as to the respective limits 

 of the Carboniferous and Permian formations, both in England J 

 and in Bohemia § ; for it cannot be denied that an accurate deter- 

 mination of genera, as well as of species, of imbedded fish- remains 

 is essential to all safe generalization as to the aspect or distinctions 

 of particular faunas, whether they be " Carboniferous " or " Per- 

 mian," and that such generalization has been seriously impeded by 

 the vague ideas hitherto prevalent regarding the genera discussed 

 in the present paper. I may therefore express a hope that the 

 observations here recorded may not be without their value, in spite 

 of the inevitable shortcomings which the nature of the subject, and 

 the limited opportunities of any one observer, forbid them being 

 without. 



* Trans. Royal Soc. Edin. vol. xiv. 1867, pp. 701-713. Also paper in Ann. 

 & Mag. Nat. Hist., quoted already. 



t Proc. Eoy. Soc. Edin. 1876-77, pp. 262-265. 



| " On the Relation of the Upper Carboniferous Strata of Shropshire and 

 Denbighshire to Beds usually described as Permian," by D. C. Davies, F.G.S. 

 (Quart. Journ. Geol. Soc. vol. xxxiii. 1877, pp. 10-28). 



§ " A Permian Flora associated with a Carboniferous Flora in the uppermost 

 portion of the Coal-formation of Bohemia," by Dr. O. Feistmantel (Geol. 

 Mag. (2) vol. iv. 1877, pp. 105-120). 



