356 Evolution and Distribution of Fishes 



As to the Albulidae, after passing seaward these evi- 

 dently spread along the warm coastal margin of Gondwana, 

 and later gave rise to the widely extended interoceanic 

 genus Albida, and the deep sea Pterothrissus. 



The Chirocentridae — including the Saurodontidae — are 

 probably derived, as stated above, from the freshwater 

 Jurassic Thrissops, and are first recorded from Neocomian 

 freshwater strata {2^1), where they are represented by 

 Chirocentrites and Spathodactylus. Chirocentriis of Sumat- 

 ran freshwater strata, (250:438) if correctly placed, 

 would then be a direct ecological representative. 



Woodward says regarding their phylogenetic affinities: 

 "The primitive nature of the Chirocentridae has long been 

 inferred from the presence of a rudimentary spiral valve in 

 the intestine of the sole surviving species Chirocentriis dorah. 

 This family of fishes is, indeed, now proved to be very 

 old, dating back at least to the beginning of the Cretaceous 

 period, during which it attained its maximum development. 

 Early Cretaceous forms, such as Chirocentrites cannot even 

 be distinguished from the typical species of the Upper 

 Jurassic Thrissops, until the cranium be available for de- 

 tailed study." 



But during Mid-Cretaceous time migration of some types 

 into the sea evidently took place, and by the close of the 

 period genera like Chiromystiis, Portheus, Ichthyodectes, 

 and Saurocephaliis had taken possession of marine stretches 

 that must have been continuous from Kansas to Central 

 Europe at least,, and which doubtless formed part of the 

 marine sea that extended between the northern Atlantis 

 continent and the southern Gondwana. The single living 

 type therefore, Chirocentriis dorah is probably a northern 

 derivative, that has migrated from the seas of China-Japan 

 into the more southerly Indian Ocean. The extensive lists 

 of these Cretaceous marine species given by Cope (25/.- 

 272-297) supplemented by those of Stewart {16^) and 

 Loomis {166) might again be mentioned. 



The Clupeidae is a family that deserves attention as 

 shedding considerable light on the main thesis of this work. 

 For some of the included species are now freshwater, some 

 are markedly anadromous, while most are purely marine. 



