OKDERS OF FISHES. 125 



scales are the chief fossil representatives of the whole class 

 of the fishes, and the order appears to have attained its 

 maximum at the present day. 



The order Teleostei is divided into the following sub- 

 orders : — 



Sub-order A. Malacopteri, Owen (= Physostomata, 

 Miiller). — This sub-order is defined by usually possessing a 

 complete set of fins, supported by rays, all of which are 

 " soft " or many -jointed, with the occasional exception of 

 the first rays in the dorsal and pectoral fins. A swim- 

 bladder is always present, and always communicates with 

 the oesophagus by means of a duct, which is the homologue 

 of the windpipe. The skin is rarely naked, and is mostly 

 furnished with cycloid scales ; but in some cases ganoid 

 plates are present. 



The more important families comprised in this sub-order 

 are the Murmnidce (Eels), the Clupeidce (Herrings), the 

 Pikes (Usocidce), the Sheat-fishes {Siluridce), the Cyprinidce 

 (Carp, Chub, Barbel, &c.), and the Salmonidce (Salmon and 

 Trout). None of these families attain any great develop- 

 ment prior to the Tertiary period, though several of them 

 appear in the Cretaceous. Thus the genus Osmeroidcs (fig. 

 494) includes Cretaceous representatives of the Salmonidm ; 



Fig. i'^i.—Osmeroides MantelK, a Salmonoid fish from the Chalk. 



the genus Felecorapis, of the same formation, may be allied 

 to the living Exoccetus ; and we may perhaps place in the 

 neighbourhood of the Pikes {Esocidce) the Cretaceous genera 

 EncJiodus, Stratodus, Pachyrhizodus, &c. The Clupeoids seem 

 also to be represented by allied forms at this comparatively 

 early period ; but the Cyprinidce. and MwmnidcB do not 

 appear till the Tertiary period is reached. From a palason- 



