SUMMARY AND CONCLUSION. 258 



same time, it appears that certain Cretaceous genera are distinctly synthetic types, 

 combining features which are characteristic even of separate families in the existing 

 fauna. The skull of Ichthyodecten, for example, is mainly similar to that of the 

 surviving Clriroceutnts, which belongs to the same or a closely-related family ; but 

 it differs in exhibiting a pit in the side of the otic region, which is now found, not 

 in the Chirocentridae, but in the Elopidas and Clupeida?. Finally, although some 

 of the Cretaceous fishes are survivors of groups which particularly characterise 

 the Jurassic period, these later forms are proved to be more highly specialised, and 

 most of them are easily distinguished from their predecessors. 



The highest types represented, although Acanthopterygians, belong only to 

 families of Berycoids and generalised Scombroids, which are always placed lowest 

 in the spiny-finned series; but it must be remembered that the English Chalk 

 fails to provide any record of the latest phase of the Cretaceous period. The 

 Danian deposits of Southern Scandinavia, which are referable to this phase, just 

 before the beginning of the Tertiary, yield Acanthopterygians of the same groups, 1 

 but one of them, Bathysoma lutheni, is very curiously specialised. The Danian of 

 Persia furnishes numerous imperfect specimens, which have been provisionally 

 interpreted as Cottoids, Grobioids, and Blennioids, 2 but they are so much crushed 

 in fissile limestone that their precise determination is impossible. The still later 

 Montian Chalk of northern France 3 and the Lameta Beds of India 4 seem to contain 

 true Percoids ; and there is a very late Cretaceous fish-bearing deposit in northern 

 Brazil 5 which may yield interesting material when exhaustively explored. None 

 of the Acanthopterygian fishes, hoAvever, hitherto obtained from these uppermost 

 Cretaceous formations reveal the initial stages in the differentiation of the modern 

 specialised groups, which appeared in the Lower Eocene and were as well defined 

 in the Upper Eocene as they are at the present day. These ancestral types 

 still remain to be discovered. 



The generalised Acanthopterygians, which are best known from the English 

 Chalk and from the Upper Senonian of the Lebanon and Westphalia, evidently 

 originated at the beginning of the Cretaceous period ; for both Aipichthys and a 

 true Berycoitl have been found at the base of the Cenomanian in Austria. 6 They are 



1 J. W. Davis, " On the Fossil Fish of the Cretaceous Formations of Scandinavia,"' Trans. Roy. 

 Dublin Soc. [2], vol. iv (1890), pp. 417—427, pis. xliii-xlvi. 



2 F. Priem, " Poissons Fossiles tie Perse," Mission de Morgan (Paris, 1908), pp. 15 — 18, pi. ii, 

 fig. 9. pi. iii, figs. 2-11. 



3 F. Priem, " Sur la Faune Ichthyologique des Assises Montiennes du Bassin de Paris," Bull. Soc. 

 Gk'ol. France [3], vol. xxvi (1898), pp. 399—412, pis. x, xi. 



4 A. S. Woodward, " On some Fish-remains from the Lameta Beds at Dongargaon, Central 

 Provinces," Pal. Indica, n.s., vol. iii, No. 3 (190-<). 



5 A. S. Woodward, " Notes on some Upper Cretaceous Fish-remains from the Provinces of Sergipe 

 and Pernambuco, Brazil," Geol. Mag. [5], vol. iv (1907), pp. 193—197, pi. vii. 



6 F. Bassani, " Descrizione dei Pesci Fossili di Lesina, etc.," Denkschr. matli.-naturw. CI. k. Akad. 

 Wiss. Wieu, vol. xlv (1882), p. 262. 



