258 FISHES 



cereal tails. They first appear in the Permian, but were only 

 abundant in the Trias and still more so in the Jurassic, while 

 in the Cretaceous the Teleostei become the dominant type. 

 The family Eugnathidoe, fishes much like a tarpon or large 

 herring in shape and fins, appear first in the Trias and are 

 common in the Jurassic ; some of them have the ganoid scaling, 

 while in others the scales are thin, cycloid, and overlapping. The 

 American Bow-fin, Amia, is a surviving member of this group, 

 retaining the incomplete vertebrae in the tail, and a bony plate 

 under the throat, which are primitive features. Caturiis and 

 Eurycormus of the Jurassic lead directly to the soft-finned 

 Teleostei (Malacopterygii) such as Tarpons (Elopidae) and 

 Herrings (Clupeidae). The latter family were already abundant 

 in Cretaceous times and are sometimes fossilised in dense 

 shoals. The Pycnodonts, deep-bodied ganoids with crushing 

 teeth, seem to have became extinct in the Lower Eocene with- 

 out leaving any descendants. Lepidosteus, the bony Pike of 

 North America (Plate XX., C), is a pike-like, predaceous modi- 

 fication of the earlier Holostei, but in the fossil condition it is 

 only known as far back as the Eocene, when it lived in Europe 

 as well as in America. 



The ancestry of the several divisions of Teleostei has not 

 yet been worked out, but it is probable that they have de- 

 scended separately from the fossil ganoids, and not all from the 

 most primitive Malacopterygii above mentioned. It has been 

 suggested that the Cat-fishes (Siluridae) were descended directly 

 from the Chondrostei, and are therefore more allied to the 

 Sturgeons than to the Malacopterygii, but it is a question 

 whether the equality of dermal rays and radials could have 

 been evolved twice independently. There seems greater pro- 

 bability that the cod-like fishes (Anacanthini) may have been 

 derived directly from the extinct Ccelacanthidse ; although the 

 latter are placed among the Crossopterygians it is remarkable 

 that the dermal rays both dorsal and ventral at the posterior 

 end of the body are equal in number to the internal radials as 

 in the Teleostei. The original termination of the tail is disap- 

 pearing, and the dorsal and ventral rays are symmetrical as in 

 the cod family (Gadidae). The chief difficulty in the hypo- 

 thesis is that in the Coelacanthidae there are two short dorsal 

 fins and one ventral whose basals are fused into a single bone, 



