484 Evolution and Distribution of Fishes 



Australia. Similarly the few known specimens of Lycoptera 

 suggest a gradual distribution during Jurassic and on thence 

 to Cretaceous time, from areas in S. Siberia on to China, 

 and then often associated with the equally widely distribut- 

 ed freshwater crustacean, Estheria m'lddendorfii. Such an 

 extensive region is that outlined by Neumayr, de Lapparent, 

 Kelloway, and Arldt (pi. 18) as the Eurasian-Australian 

 continent. This continuity may not have been coeval in 

 all of its constituent land-parts, but even a make-and-break 

 action must have left ways and means for steady migration 

 of the genera above-named. If we were acquainted more 

 fully however, with the fossil fishes of South Siberia, China, 

 Siam, New Guinea, and Australia, which lived during that 

 time, the evidence would be more satisfactory. 



But one or two allied genera to the above seem not only 

 to favor such a land-connection, they suggest either a con- 

 tinuous or interrupted connection back to Triassic times. 

 Thus Pholidophorus, in its known species, extends from 

 Purbeck and Kimmerldgean beds down to those of the 

 Lower Lias; while if such species as P. fiircatus, P. {Balei- 

 ichthys) sibiricus, P. gregarius,, and P. dubius are truly 

 referable to this genus, they indicate distribution for the 

 genus from Britain through Central and S. Europe on by 

 Siberia to Australia. But the connection between central 

 and S. E. Asia with Australia seems to have broken up to- 

 ward late Jurassic or early Cretaceous time, so that these 

 two areas were probably quite apart till mid-tertiary time, 

 when reestablishment of a rather short-lived connection 

 permitted the passage northward into E. Asia of the most 

 evolved types of marsupials (p. 446) and the intermingling 

 of genera belonging to various plant families. 



Meanwhile In connection with, and so far confirmatory 

 of, results already set forth for higher teleosts, we may 

 next gather information from the aethiospondyiic Holo- 

 steans, a group that is made up of the genera Lepidosteus 

 that still survives — and of the two fossil genera Belonosto- 

 mus and Aspidorhynchus. The first of these includes five 

 living species that occur over the N. American continent 

 southward to Central America. But the genus can also be 

 traced back in the West to the Bridger beds of lower Eocene 



