FISH. 



nsif. 





ml PolfpKrui; the Pyettodonta, likewise fotdl; the Scltrodtrmi, 

 GymuadoiUtt, Lopkobrmckii, Goniodoatet, SUnrida, and Sturuma. 



la the third order, Ctatoidet (from KTIHH, a oomb), the scale* consist 

 of lamina whose posterior and free margin it pectinated. A struc- 

 ture very evident in the Chtetodons and Flat- Fishes (PUnronrcti<ltt), 

 which M. Agassi* thinks ought to be placed close together. In this 

 order are also arranged the Percida, Polyacanthet, Sciamuhr, Sparida, 

 Scorpmuda; and A /* ow*. 



Order four, Cyttoidtt (from KA<M, a circle). The families which 

 belong to thia order have the scale* formed of simple lamina;, with 

 the posterior margin smooth. The scales of the lateral line are 

 formed like the others, but instead of flat laminae they consist of 

 ducts placed one within the other, of which the retiring portion, 

 which is applied against the disc of the scale, forms the tube through 

 which flows the mucous secretion which covers the fish. This tube is 

 sometimes bifurcate, or even ramified. The Labrida, Mugilidtr, 

 Atkerina, Scombrida, Gadida, Gobiada, Muramida, Lucioida, Salmo- 

 ni<l<e, Clupei<l<r, and Cyprintda belong to this tribe. 



In his work entitled ' Kecherches sur les Poissons Fossiles' 

 M. Agas*iz has employed this arrangement in his description of Fossil 

 Fishes. At the request of the British Association for the Advance- 

 ment of Science, M. Agasaiz has drawn up a list of fishes occurring in 

 the British strata, and } we subjoin an abstract of this report The 

 geological classification' is that developed in the articles PAL.EOZOIC 

 SERIKS and SALIFKROUS SYSTEM. 



TABLE I. General 2>ittribution of Ike Orders of Fossil Pithtt. 



Hence it appears that the two orders of Ctenoid and Cycloid Fishes, 

 which are the most abundant in existing nature, have no representa- 

 tives yet discovered in the Palscozoic Strata. 



If we divide the two groups of Mesozoic and Palrcozoio Strata into 

 their constituent parts we shall have additional results. 



TABLE ll.Dittribulion of the Ordert of Pottil Fitha in Maozoic and 

 Paleozoic Strata. 



Hence it would appear that the Placoid Fishes (Onckut, &c.) are, 

 geologically speaking, the most ancient of the finny races ; that the 

 Ganoid Fishes, Jloloptychiut, &c., begin in the middle Palaeozoic 

 series, and the Ctenoid and Cycloid only in the upper Mesozoic 

 (Cretaceous) group. It is however very possible that this last statement 

 may be modified by further research in the Oolites. At present the 

 distribution of Ctenoid and Cycloid Fishes in the Chalk is thought to 

 favour the notion of the almost Cainozoic character of that deposit. 



In the next four tables (Tables III., IV., V., and VI.) we give the geo- 

 logical distribution of the several families (some are merely provisional) 

 under which II. Agassiz has ranged the British Fossil Placoid Fishes. 



TABLK lll.Dutribiition of lite Pamiliu of Placoid Fuhet. 



Hence the most prolific periods for Placoid Fishes seem to bo the 

 upper PaUcozoic, the middle and upper Mesozoic, and the lower 

 Cainozoic strata. 



IV.DitlrUjution of the Familia of Ganoid Fithti. 



The Ganoid Fishes (singular forms however) begin to abound in Uio 

 middle Palicozoic series, and become rare above the lower CiiiuoAiic 

 series. They are also rare in existing nature. M. Agassiz once 

 included the Glyptocepkalut of Sheppey among the Ganoids, but in 

 his later catalogue he has joined it to the Cycloids. 



TABLE V. Distribution of the Familiet of Ctenoid Pallet. 



CAIN.,/. ii. : 

 Upper 

 Middle 

 Lower 



MESOZOJC : 

 Upper 

 Middle 

 Lower 



r \ i i .1 i/i M i : 

 Upper 

 Middle 

 Lower 



I 



The account of the Ctenoid Fishes in the lower Cainozoic Strata ia 

 from the report of M. Agassi/, to the British Association in 1844. 



TABLE VI. Dulribution of the Familia of Cycloid FMei. 



To complete thia view of the geological distribution of Fossil Fishes 

 we append an abstract of the catalogues of M. Agassiz, which have 

 been already referred to. 



Silurian Syttem. 



PLACOID FISHES. 



Ichthyodorulites. 

 Oncltiu, 2 species. 



Family unknown. 

 Thelodtu, 1 species 

 Sclerodva, 1 species. 

 Plectrodtu, 2 species. 

 Xl'hnyodiu, 1 species. 



Pteryyotui, 1 species. (This 

 probably a Crustacean.) 



Devonian Ft/stem. 



PLACOID FISHES. 



Ichthyodorulites. 

 Onchut, 2 species. 

 Parcfva, \ Hpecics. 

 Ctenacanthut, 1 npccips. 

 Ptt/akacan&mt, 1 specie 

 Cicmalint, I species 



