ETHEOSTOMATID^. 13 



6. Upper jaw not protractile ; vomerine teeth present : 

 c. Mouth narrow, inferior, overlapped by a tapering, truncate, naore or less pijj- 

 like snout ; ventral plates present, or, if fallen, a naked strip; body elon- 

 gated ; cheeks and opercles scaly ; size largest of all the darters, Percina, 3. 

 cc- Mouth wider, terminal, the upper jaw being but little longer than the lower: 

 d. Ventral plates developed, or, if fallen, middle line of belly with a naked strip : 

 e. Body and head elongate ; the vertebra in increased number, more than 

 20 in front of anus ; well-developed teeth on vomer and palatines ; dorsal 



spines 12 to 15; fins never tuberculate Alvordius, 4. 



ee. Body and head shortened; vertebra) fewer, less than 20 in front of anus; 

 a few minute teeth on vomer and none on palatines ; dorsal spines 10 to 

 12 ; colors brilliant, the male in spring with the lower fins tuberculate, 



Ericosma, 5. 

 dd. Ventral plates not developed ; middle line of belly scaled like the sides, 



Hadropterus, 6. 



hb. Upper jaw protractile, a distinct furrow separating it from the skin of the 



forehead : 



/. No ventral plates ; posterior ventral region scaled ; anterior region largely 



naked ; vomer well toothed ; head and body stout and heavy ; cheeks 



and opercles scaly ; anal fin (in adult males ?) greatly elevated, reaching 



to base of caudal fin Imostoma, 7. 



//. Ventral plates well developed, or, if fallen, a naked strip ; vomer with a few 

 minute teeth; palatines naked; body rather slender, with rather narrow 

 head and smaller subinferior mouth ; cheeks naked ; opercles scaly ; anal 



fin not enlarged Rheocrypta, 8. 



*i. Second dorsal considerably larger than anal fin ; no ventral plates, the middle 

 line of the belly always covered with small scales like those of the sides : 

 g. Upper jaw protractile : 



h. No teeth on vomer or palatines ; mouth small, contracted, subinferior ; head 

 short and thick, with swollen cheeks ; spinous dorsal rather long ; cheeks 

 and opercles scaly ; anal spines strong ; body elongated, little compressed, 



DiPLESIUM, 9. 

 hh. Vomerine teeth present ; dorsals contiguous, but distinct ; the spinous dor- 

 sal short ; head narrowed ; the mouth rather small, horizontal, sub- 

 inferior : 



i. Anal spines two, well developed; the first the longer. Arlina, 10. 



a. Anal spine single, more or less obscure and undiiferentiated from the soft 



rays Boleosoma, 11. 



gg. Upper jaw not protractile : 

 j. Dorsal fins well apart; body fusiform, little compressed ; scales large; cheeks 

 and opercles scaly; mouth small, horizontal, subinferior (as in Boleosoma) ; 



caudal peduncle rather slender Nanostoma, 12. 



jj. Dorsal fins slightly connected at base ; body rather short, deep, strongly 

 compressed ; scales small ; cheeks naked ; mouth rather large, oblique 



(as in Poecilichthi/s) ; caudal peduncle deep Nothonotus, 13. 



**. Lateral line incomplete or wanting ; no ventral plates ; upper jaw not protractile ; 



second dorsal larger than anal ; vomer with teeth : 

 Jc. Lateral line present on anterior part of body : 



I. Dorsal fins contiguous, the membrane of the first reaching to the base of the 

 second: 

 m. Spinous dorsal fin well developed, two-thirds or more the height of the 

 second ; the spines graduated, never ending in little fleshy knobs ; lateral 

 line extending more than half the length of the body ; mouth moderate, 

 the upper jaw usually a little the longer; opercles scaly; cheeks naked; 

 body rather short and deep Pcecilichthys, 14. 



