TELEOSTS. 259 



ably developed from isospondylous ancestors, possibly by way of 

 two or more lines, one of them apparently being the Haplomi. 

 Among the more primitive stocks are percesoces and the salmo- 

 percse, and from these and possibly other groups, the others have 

 descended. In order that the various families may be arranged 

 in some accordance with their affinities these two sub-orders 

 have been somewhat widely separated. 



Sub-Order i. Salmoperce. 



Acanthopteri with adipose fin, dorsals and anals spined ; ventrals 

 abdominal, ctenoid scales ; duct of air-bladder persistent. 



A structurally primitive group but no fossils known. Only genus 

 Percopsis, with its centre in the great lakes. From this sub-order we fol- 

 low out first what may be called a percoid line. 



Sub-Order 2. Xenarchi. 



Acanthopteri with a single dorsal fin, ventrals thoracic, air-bladder 

 large, anus at the throat. Contains only the family of pirate perches with 

 one species {Aphredoderzes sayanus) of the U. S. Erismatopterus and 

 Ainphiplaga from the eocene of Wyoming. 



Sub-Order 3. Percoidea. 



Ventrals with one spine and five rays; lower pharyngeals separate; 

 nostrils double, scales ctenoid. Percid^, scales extending but a short 

 distance on the vertical fins ; lateral line continuous ; palatines with teeth ; 

 fresh water. Elassoma, Lepomis, (sunfish), Micropterus (black bass), 

 Etheostoma (darters), Perca (perch). Closely allied are the marine Ser- 

 KANNID^E ; Hcemtilon, Priacanikus, etc. Perca dates from the oligocene, 

 Serranits from the miocene, Erismatopterus, eocene. SpariDjE, salt-water 

 perches, teeth of the jaws either for. cutting, or molars, the palate usually 

 toothless. Sargiis, represented by the American sheepshead, dates from 

 the miocene. Lutjanus. ScIjEnid^e, Cynoscion, weak fish. 



Sub-Order 4. Loricati (Cataphracti). 



Body frequently armored with bony keeled scales or plates ; a bony 

 process — the suborbital stay — extends across the cheek from the infraor- 

 bital ring to the preoperculum. The ScorPjEnid^, or rock-fishes, are the 

 most perch-like ; Scorpana, European ; Sebastes, the Norway haddock. 

 The living species are marine, Scorpcena appearing in the miocene, Petalop- 

 tervx in the cretaceous. Cottid«, sculpins, body naked or covered with 

 irregularly arranged scales ; usually two dorsals, anal without spines. A 

 few, like Uranidea and Cottus, occur in fresh water; but the larger forms, 



