No fossil species of Pegasidæ are known.
CHAPTER XIV
SALMOPERCÆ AND OTHER TRANSITIONAL
GROUPS
Suborder Salmopercæ, the Trout-perches: Percopsidæ.—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 Salmopercæ. This is characterized by the presence of the adipose fin of the salmon, 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 Percopsidæ would seem to find its place in Cretaceous rocks rather than in the waters of to-day.
Fig. 191.—Sand-roller, Pecropsis guttatus Agassiz. Okoboji Lake, Ia.
Percopsis guttata, the trout-perch or sand-roller of the Great Lakes, is a pale translucent fish with dark spots, reaching a length of six inches. It abounds in the Great Lakes and their tributaries and is occasionally found in the Delaware, Ohio, Kansas, and other rivers and northwestward as far as Medicine Hat on the Saskatchewan. It is easily taken with a hook from the piers at Chicago.
Fig. 192.—Oregon Trout-perch, Columbia transmontana Eigenmann. Umatilla River, Oregon.
Columbia transmontana is another little fish of similar type, but rougher and more distinctly perch-like. It is found in sandy or weedy lagoons throughout the lower basin of the Columbia, where it was first noticed by Dr. Eigenmann in 1892. From the point of view of structure and classification, this left-over form is one of the most remarkable of American fishes.