Catalogue of Fossil Fishes. 135 



account of the Jurassic ganoids, or those Actinopterygian Teleostomi 

 that were dominant during the deposition of the first half of the 

 Secondary rocks, and includes such genera as Chondrosteus, Semionotus, 

 Lepidotiis, Dapedius, Euynathus, PacTiycormus, and Fholidophorus. 

 Many forms of Pycnodonts are described both from Jurassic and 

 Cretaceous rocks, while Zophiostomiis and Protosphijrcena are repre- 

 sentative genera of Cretaceous age. Amia and Lepidosteus are 

 Tertiary types of these fishes which have continued to exist to the 

 present day. 



The fishes which remain for consideration are just those which 

 have for so long been known as Teleosteans, or true bony fishes, 

 and the fourth volume of the work, now published, is really an 

 account of the Bony Fishes of the Cretaceous and Tertiary formations. 



The present volume begins with Isospondylous Actinopterygii ; 

 that is, those fishes with non-lobate fins, which have vertebra more 

 or less ossified, without indications of pleurocentra or hypocentra, 

 and having none of them fused together ; the lower jaw also is 

 formed of only two or perhaps thi-ee distinct bones. The three 

 families of these fishes which have the closest affinities with the 

 old-time ganoids, were included with those forms in the previous 

 volume. 



Among the remaining families of the Isospondyli are to be found 

 many remarkable genera of Cretaceous bony fishes ; and these, with 

 tlie other suborders, may now be considered more in detail. The 

 Isospondyli include among them the Elopid^ and Chirocentridse, 

 which are " the most important Cretaceous families of primitive 

 bony fishes " ; they were at that period particularly abundant and 

 widely distributed, and a few of their descendants are living at 

 the present day. The Elopidee are of especial interest, inasmuch 

 as they retain the gular plate, so characteristic in Jurassic fishes, 

 and here appearing for the last time ; indeed, in some of the genera 

 it is quite rudimentary. Isteus is a noteworthy genus, on account 

 of its close relationship with the living deep-sea Bathythrissa. 



In the Cretaceous period were many and striking forms allied 

 to the living but primitive Chirocentrus ; among these may be 

 mentioned the giant Fortheus of North America, which is represented 

 also in this country by more than one species. Tlie well-known 

 Saurodon and Saurocephalus are likewise members of this family, 

 and Dr. Smith Woodward regards the Thrissops of the Upper 

 Jurassic as a near ally. 



Some years ago, it will be remembered, the reptilian jaw which 

 Owen called Mosasaurus gracilis, now in the Brighton Museum, 

 was relegated to the piscine genus Pachyrhizodus, of the family 

 Elopidse ; it is pleasing, therefore, to know that a renewed examination 

 of the type shows the correctness of Owen's determination, and that 

 this specimen is to return to its place among the Mosasaurian reptiles. 



True Clupeoids are well represented in the Cretaceous rocks, " and 

 their skeleton is so closely similar to that of the typical Jurassic 

 Leptolepidse that they may well be direct descendants of the latter. 

 . . . . Most of the Cretaceous forms are typical Clupeidas, and 



