110 



Actinopterygii IsospondyH. 



being invested with thin and flexible, deeply-overlapping scales 

 which are either smooth ("cycloid," Fig. 156A), or pectinated 

 ("ctenoid," Fig. 156B), at the hinder margin. 



Next to the Leptolepidee are arranged the representatives of 

 the lowest of the truly bony fishes which still survive, namely, 

 the herring-like family Elopidae, which comprises several genera 

 exhibiting a gular plate like that of Amia. Among these, the 

 finest are the examples of Osmeroides and Aulolepis from the 

 English Chalk, long supposed to be Salmonidae. Theories in 

 the table-case includes the type-specimens from the collection 

 of the late Dr. Mantell, and several beautifully worked out of the 

 chalky matrix by this distinguished pioneer in palaeontology. 

 Those of Osmeroides are especially perfect, and, like most fossil 

 fishes from the Chalk, they are almost uncompressed, the fine 

 calcareous particles having replaced the muscular and other 

 tissues as rapidly as they were destroyed by decomposition, thus 

 preventing the collapse of the flanks, and preserving the natural 

 rotundity and form of the fish when living. Other closely- 

 related genera are Thrissopater from the Gault of Folkestone, 

 and Ehacolepis in nodules from the Upper Cretaceous of 

 Brazil. 



The Clupeidse, or herrings -proper, date back to the Cretaceous, 

 where thev are represented both in Mount Lebanon and 



FIG. 157. Dlploniystus brevissimu*, Blainv. sp. (after Pictct and Humbert) ; Upper 

 Cretaceous, Mount Lebanon. 



Brazil by Diplomystus (Fig. 157), which only seems to differ 

 from the modern Clnpea in the possession of a series of 

 scutes between the back of the head and the dorsal fin. This 

 fish is also common in the European and North American Lower 

 Tertiaries, and still survives in the rivers of Chili and New 

 South Wales. Clupea itself may date back to the Eocene, but 

 this is uncertain. Scombroclupea (with finlets behind the anal), 

 Rhinellus (Fig. 158), Leptoxomus, Chirocentrites, and other fishes 

 from Mount Lebanon, are also believed to be Clupeoids. 



It is interesting to notice that in the Syrian area, owing to 

 ;some physical change in the conditions of the sea at the time 

 the Cretaceous deposits were being laid down, these fishes 



