PHYLUM CHORDATA 



243 



Among Teleostei the Physostomi are largely, though not 

 exclnsively, fresh-water Fish ; the Carps, Eels, Salmonoids, and 

 Siluroids are important examples. The Acanthopteri, Pliaryngo- 

 gnathi, and Anacanthini are mostly marine, some being in- 

 habitants of the shores, some pelagic, some abyssal, extending 

 to a depth of nearly 3,000 fathoms. As we have seen, many 

 species are practically terrestrial. AH the sub-orders are uni- 

 versally distributed, so that we have to descend to families before 

 meeting with any important facts in geographical distribution. 



The Distribution in Time of the Teleostomi is interesting 

 as showing the gradual replacement of the lower or more 



F^hr 



Fio. 900.— A, restoration of Glyptolepis (Devonian) ; B, IMCacropoma matitelli (Cretaceous). 

 a. hi. ossified air-bladder ; d.f. l,d.f.^, dorsal fins; li. a. hsemal arches ; jug. pi. jugular plates ; 

 n. a. neural arches ; nch. position of notochord ; pet. f. pectoral fin ; pv. f. pelvic fin ; v. f. 

 ventral fin. (From Nicholson and Lydekker.) 



generalised members of a group by the higher or more specialised 

 forms. During the whole of the Paleeozoic and the greater part 

 of the Mesozoic era the three orders of Ganoids, to-day small 

 aiid isolated groups, formed the whole of the Teleostomian fauna, 

 and it is not until the Cretaceous period that the Teleostei, the 

 present dominant order, make their appearance. From the Cre- 

 taceous onwards the Ganoids undergo a progressive diminution 

 in numbers, genus after genus and family after family becoming 

 extinct, while a corresponding increase takes place in all the sub- 

 orders of Teleostei. 

 The Crossopterygii make their first appearance in the Devonian 



