CHAPTER XIV 



SALMOPERCLE AND OTHER TRANSITIONAL 



GROUPS 



UBORDER Salmopercae, the Trout-perches: Percopsidae. 

 More ancient than the Hemibranchii, and still more 

 distinctly in the line of transition from soft-rayed to 

 spiny-rayed fishes, is the small suborder of Salmoperccz. This 

 is characterized by the presence of the adipose fin of the salmon, 



FIG. 191. Sand-roller, Pecropsis guttatus Agassiz. Okoboji Lake, la. 



in connection with the mouth, scales, and fin-spines of a perch. 

 The premaxillary forms the entire edge of the upper jaw, the 

 maxillary being without teeth. The air-bladder retains a 

 rudimentary duct. The bones of the head are full of mucous 

 cavities, as in the European perch called Gymnocephalus and 

 Acerina. There are two spines in the dorsal and one or two 

 in the anal, while the abdominal ventrals have each a spine and 

 eight rays. Two species only are known among living fishes, 

 these emphasizing more perfectly than any other known forms 

 the close relation really existing between spinous and soft- 

 rayed forms. The single family of Percopsida would seem to 

 find its place in Cretaceous rocks rather than in the waters of 

 to-day. 



ii 16 



241 



