. A guide to the study of fishes. Fishes; Zoology; Fishes. 3 lO Percoidea, or Perch-like Fishes and especially abundant at the confluence of rivers. Gymno- ccphalns schrcrtzer of the Danube has the head still more cav- ernous. Percarina demidoffi of southern Russia is another dainty little fish of the general type of the perch. A fossil genus of this type called Smerdis is numerously represented in the ]\Iiocene and later rocks. The aspron, Aspro asper, is a species hke a darter found lying on the bottoms of swift rivers, especially the Rhone. The body is elongate, with the paired fins highly
. A guide to the study of fishes. Fishes; Zoology; Fishes. 3 lO Percoidea, or Perch-like Fishes and especially abundant at the confluence of rivers. Gymno- ccphalns schrcrtzer of the Danube has the head still more cav- ernous. Percarina demidoffi of southern Russia is another dainty little fish of the general type of the perch. A fossil genus of this type called Smerdis is numerously represented in the ]\Iiocene and later rocks. The aspron, Aspro asper, is a species hke a darter found lying on the bottoms of swift rivers, especially the Rhone. The body is elongate, with the paired fins highly developed. Zingel zingel is found in the Danube, as is also a third species called Aspro streber. In form and coloration these species greatly resemble the American darters, and the genus Zingel is, perhaps, the ancestor of the entire group. Zingel dift'ers from Percina mainly in having seven instead of six branchiostegals and the pseudobranchiae better. Fig. 243.—The Zingel, Zingel zingel (Linnaeus). Danube River. (After Seelye.) developed. The difiierences in these and other regards which distinguish the darters are features of degradation, and they are also no doubt of relatively recent acquisition. To this fact we may ascribe the difficulty in finding good generic char- acters within the group. Sharply defined genera occur where the intervening types are lost. The darter is one of the very latest products in the evolution of fishes. The Darters: Etheostominae. — Of the darters, or etheosto- mine perches, over fifty species are known, all confined to the streams of the region bounded by Quebec, Assiniboia, Colo- rado, and Nuevo Leon. All are small fishes and some of them minute, and some are the most brilliantly colored of all fresh- water fishes of any region, the most ornate belonging to the large genus called Etheostoma. The largest species, the most primitive because most like the perch, belong to the genus Please note that these images are extracted from s
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