358 On the Age of the Sandstones of the Newark Group. 



was founded npon a careful comparison of the genus Catopterus 

 with the fossil fishes of different formations in Europe, as these 

 are portrayed in the great work of Prof. Agassiz, then recently 

 received. Such portion of the description and observations 

 then made as relate directly to the geological age of the forma- 

 tion are here quoted. 



Of the genus Catopterus, species C. gracilis, he says: — "Tail 

 forked, equilobed. Scales extending a little upon the base of 

 the upper lobe." And in regard to the equilobed tail, he adds 

 in a subjoined note : — " This indeed is not strictly the case. Its 

 structure, however, is analogous to that of the Semionotus, 

 ranked by Agassiz among the Homocerci, and differs most deci- 

 dedly from that of the true Heterocerci, where the scales, and 

 probably the vertebras, extend to the extreme point of the upper 

 lobe." He adds : — 



"In the arrangement of Agassiz, this fish would be compre- 

 hended in the order Ganoides, and family Lepidoides. Its equi- 

 lobed tail would assign it to the second division of the family, 

 the Homocercj, as he has termed them. From seven fusiform 

 genera now arranged in this division it is entirely excluded by 

 the posterior position of its dorsal. It may therefore be ranked 

 between the genera Semionotus and Pholidophorus, being analo- 

 gous to both in the structure of the tail, and in its serrated fins, 

 and to the latter in the articulation of the rays. From the situ- 

 ation of the dorsal fin I have thought the name Catopterus to be 

 applicable to this new genus." — Annals Lyc. Nat. Hist. vol. iv, 

 pp. 38-39. 



Nearly twenty years have elapsed since the promulgation of 

 these careful and apparently conclusive observations, which do 

 not appear to have been weakened or set aside by any subse- 

 quent researches. It is proper to state that the two analogous 

 genera above mentioned are found in the Oolitic series as well as 

 in the Lias, and it is believed that few, if any of the kindred 

 genera have a lower range.* The above observations afford at 

 least sufficient warrant for the cautious and perhaps too limited 



* A single case of semi-heterocercal structure as occurring in the coal rocks of 

 Autun in France, was mentioned to us by Professor Agassiz in 1846. As we learn 

 nothing more of its appearance in the palaeozoic series, may there not possibly be 

 an error as regards the authenticity or position of this fish ? If otherwise it does 

 not seem to have appeared again until after the Permian period. On the other 

 hand, it appears to be admitted that the true heterocerques, of the Palceonzscus 

 type, do not appear above the Trias, and I think they are not found above the Per- 

 mian. 



It should be noted that Sir. P. Egerton has described a most singular fish from 

 the upper strata of the New Red, of a genus hitherto unknown, which has but little 

 inequality in the structure of its caudal base. This fish, the Dipteronotus cyphas 

 Eg., is very short and broad, with a double dorsal, and is altogether so unique in its 

 character that its occurrence may be deemed to affect but little the chronological 

 inferences which are drawn from the varied structure of the numerous genera and 

 species of the Lepidoid family. — See Geol. Jour. 1854, p. 369, with a figure. 



