122 VERTEBRATE ANIMALS OF THE UNITED STATES 



bi Parietal region of skull flattened or depressed. 



Ci Snout projecting beyond the mouth 3. Percina. 



C2 Snout not projecting beyond the mouth. 



di Body compressed, not hyaline or extremely 

 elongate. 

 Ci PremaxUlaries not protractile. 



fi Midventral line with enlarged scales or scale- 

 less 4. Hadroptcrus. 



i-i Scales in the midventral line like those on 



the sides of the body 5. Hypohomus. 



e2 Premaxillaries protractile, 

 fi Anal spines 2. 



gi Ventral fins well separated 6. Cottogasier. 



g2 Ventral fins close together. 



hi Vomer teeth present 7. Ulocenira. 



h2 Vomer teeth absent 8. Diplesion. 



f2 One anal spine present 0. Bolcosonia. 



d2 Body depressed, hyaline and very elongate. 



ei Premaxillaries not protractile 10. Crystallaria. 



€2 Premaxillaries protractile. 



fi One anal spine present 11. Amniocrypta. 



U Anal spines 2 12. loa. 



hz Parietal region of skull convex; belly with ordinary scales; 

 ventral fins close together. 

 Ci Lateral line wholly or partially present, 

 di Lateral line straight. 



ei Head naked above 13. Etheostoma. 



62 Head scaly above 14. Psychromaster. 



d2 Lateral line arched towards the back. 



Ci Head scaly above 15. Copdandellus. 



62 Head naked above 16. Boleichthys. 



C2 Lateral line wanting 17. Microperca. 



I. Perca L. Body elliptical, compressed; cheek scaly; opercle 

 mostly naked and armed with a single spine; preopercle serrated; mouth 

 terminal; branchiostegals 7; pseudobranchiae small, but well developed; 

 pyloric caeca 3; caudal margin concave: 3 species, P . fiuviatilis occurring 

 in Europe, and P. schrenki in Asia. 



P. flavescens (Mitchill). Yellow perch; common perch. Length 

 300 mm.; head 3.25; depth 3.25; back elevated; color dark olive green 

 above; sides yellow with 6 to 8 broad dark transverse bars; belly bright 

 yellow; lower fins orange; rays of dorsal fins XIII to XV-II, 13 to 15; 

 anal II, 7 or 8; scales 7-74 to 88-17: Nova Scotia to North Carolina, in 

 coastwise streams; throughout the Great Lakes region and westward to 

 Iowa and Dakota; not found from central Ohio southwestward; very 

 common; introduced on the Pacific slope. The perch spawns in the 



