The Spine-finned Teleostei 397 



differences in structure, due to the continuous action of the 

 varied factors that together constitute the fundamental 

 law of Pentamorpliogeny. (/: 174). 



The series of families which by Boulenger has been 

 called the Scleroparei shows, in such of them as the Scorpae- 

 nidae and Hexagrammidae, very direct and marked affinity 

 with some of the Serranidae. But such seem decidedly 

 apart from the Cottidae, the Cyclopteridae, the Agonidae, 

 the Trigulidae and the Dactylopteridae, not least in the 

 absence amongst the latter of spines to the many-rayed anal 

 fin. The distribution also is highly perplexing. For while 

 the entire series belongs to the northern temperate hemi- 

 sphere, the first-named two families are purely marine, 

 while the Cottidae and Comephoridae Include freshwater 

 species of wide distribution. Thus 8 out of the 28 species 

 of Cottus are wholly freshwater, and 3 of the 10 species 

 of Centridermichthys are. In regard however to probable 

 absorption of the three anal spines that are so typical of 

 Serranidae and of most Scorpaenidae, it should be noted 

 that reduction to 2 or i, or even total absorption of the 

 spines, is seen going on in some Hexagrammidae {e. g. 

 Zaniolepis) and in some Comephoridae. It may be that 

 the Cottidae and Comephoridae are derivative from some 

 primitive freshwater Serranid, and passing seaward de- 

 veloped the Agonidae, the Cyclopteridae, and allies. But 

 it seems Impossible as yet to correlate the geographic distri- 

 bution with the structural aflSnltles shown. 



The wholly marine alliance of families that by recent 

 Ichthyologists has been grouped as the Scombrlformes, in- 

 cludes about nine families widely distributed over tropical, 

 subtropical and temperate seas. These are the Carangidae, 

 Rhachlcentridae, HIstiophoridae, Scombridae, Luvarldae, 

 Coryphaenidae, Xiphlldae, Bramldae, and Trichlurldae. 

 These seem to come off from some ancient marine forms 

 of the Serranidae, distinct from, though related to, types 

 like those that originated the Pseudochromldae and near 

 allies. The Carangidae show marked generic variations, 

 that might indicate descent of its genera from several dis- 

 tinct Serranid genera. Thus Anthias, Odontanthias and 

 Holanthias of the Serranidae have combined characters 



