Summary of Conclusions Reached 525 



And throughout it Is shown that freshwater teleosts are 

 nearly always the primitive and environally ancestral 

 groups , while the marine ones are derivative and more 

 evolved. 



Chapter 13. The spine-finned Teleostei in tiine and space. 



Study of these recalls Jordan's observation that in 

 Sticklebacks an increasing number of fin-spines develops 

 as these pass from a freshwater to a marine environment. 

 In transition from certain of the soft-rayed to the hard or 

 spiny-rayed teleosteans the writer accepts such a series as 

 the Clupeidae, Salmonidae, Percopsidae and Berycidae 

 as furnishing needed types. Thus Diplomystus, Salmo, 

 Percopsis, Acerina and Aphredoderus among living forms ; 

 also Asineops, Erismatopterus and Trichophanes amongst 

 fossil ones, are strikingly graded in series. But in process 

 of evolution three divergent lines of modification seem to 

 have arisen. One ended in the highly specialized Pantodon 

 of W. Africa; a second became marine as the Ctenothriss- 

 idae; a third and highly important one led from Percopsis 

 and Columbia through the Aphredoderidae to the Percidae 

 or perches. These are illustrated in their transition details. 



The Percidae and nearly allied Centrarchidae seem, in 

 early Eocene time, to have sent off into the sea the two 

 marine alliances the Beryciformes and Scombriformes. But 

 meanwhile the large families Cichlidae, Nandidae, Serran- 

 idae, and Lobotidae developed in lakes and rivers, except 

 that the two last families gave off genera which passed 

 seaward. But, as traced in detail, the Chaetodontiformes, 

 Scorpaenidae, and Gobiiformes also passed seaward from 

 freshwater Percidae, and then often underwent striking 

 structural modifications. The changes undergone in the 

 positions of the paired and unpaired fins are then traced 

 in the above families, and these are shown to have a definite 

 relation to their evolution and distribution. The great centre 

 of origin and even of evolutionary change is regarded as 

 the western lake area of N. America, and this during Cre- 

 taceous to Eocene time. The distribution of the main groups, 

 and also of the important genera of each group, from the 

 above region as a centre is traced. 



