50 THOMAS SAY FOUNDATION 



Costal edge of wing not yellow (except in Perla 

 capitata) : fusion of veins Rs and M in hind wing 

 less extensive (except in Clioperla annecta) 13 



13. Male with a percussion disc or hammer developed 



on the 9th abdominal sternite; large species 

 with copious venation, and usually many cross- 

 veins in the portion of the wing beyond the 

 cord ; cubito-anal crossvein close to the apex of 



the anal cell icroneuria 



No percussion disc on the 9th sternite of the 

 male (except in Perla languida) 14 



14. The 10th abdominal segment of the male cleft 



above; genital hooks when present developed 



from the apical angles of the cleft Perla 



The 10th abdominal segment entire above ; geni- 

 tal hooks when present developed from the sub- 

 anal lobes Clioperla 



Genus PERLODES Banks. 



1903. Perlodes Banks, Ent. News, 14:241. 



1912. Perlodes Klapalek, Coll. Zool. de Selys, IV, 1:31. 



1841. Dictyopteryz Pietet, Hist. Nat. Perlides, p. 147. 



1917. Perlodini Smith, Trans. Amer. Ent. Soc, 43:46.3. 



Rather large, dusky-winged stoneflies, having an area 

 of irregular polygonal cells .in the front portion of the 

 wing tip beyond the well developed cord. Crossveins in 

 the costal space tend to be reduced in number, and some- 

 times almost absent especially from the portion adjacent 

 to the humeral crossvein. The first anal vein in the fore 

 wing where it departs from the anal cell is bent forward 

 to its junction with the cubitus, and then suddenly bent 

 away again at a sharp angle. The basal fusion of veins Rs 

 and M in the hind wing is short. There is a longitudinal 

 middorsal pale line on the prothorax, that is often con- 

 tinued forward upon the rear of the head, ending in a yel- 

 low spot within the ocellar triangle and there is a pale M- 

 mark across the frons before the ocelli. The basal seg- 

 ment of the tarsus is about twice as long as the second 

 and a third as long as the third segment. Tails Ion? and 

 hairy. Ventral gill rudiments persist in about half the 

 species in from one to five pairs, the foremost of which is 

 found at the base of the labium. 



Genital hooks are developed in the male from the rear 

 portion of the divided tergum of the tenth abdominal seg- 

 ment. In a deep cleft between these the chitinous U- 



