198 A YEAR OF COSTA RICAN NATURAL HISTORY 



tlons. The other exclusively waterfall-dwelling dragonfly 

 that we found at Juan Viiias, Argia talamanca, belongs to a 

 genus distributed from Canada to Argentina. Many species 

 of Jrgia occur in Costa Rica, but only talamanca appears 

 to have adopted this peculiar and restricted place of abode 

 throughout its entire life. A. found a pair of talamanca at- 

 tempting to oviposit in the mud on the hard rock face of 

 the nearer waterfall on July 27. On August 3, an exuvia 

 of this species was found on the vegetation to one side of the 

 main stream of the same fall, but on the perpendicular face 

 where there was constant dripping, and immediately above 

 and resting on it, was the male which had just emerged. 

 Single males were found at or near one or the other of these 

 two falls on June 24, September 28 and December 2. Larvae 

 which corresponded with the exuviae of August 3 were ob- 

 tained in March. 



Argia talamanca is a slender dragonfly one and three- 

 eighths inches long, whose clear wings extend about two in- 

 ches. The male has a pale blue thorax with a black line down 

 the middle of its back and two black stripes on the sides, 

 while the abdomen is chiefly black with pale blue at both 

 ends. The female tends to replace the blue with more vio- 

 laceous tints, the middle black line of the thorax is widened 

 into a stripe and the pale blue near the hind end of the ab- 

 domen is limited to one segment (the eighth) instead of 

 covering three. Another species of Argia was met with at 

 these waterfalls but was not restricted to them. This was 

 A. underwoodi, slightly larger than talamanca, resembling 

 it in colors but difi"ering in details of structure and in the 

 male having the middle black stripe on the thorax wider so 

 that black predominates there. We did not obtain the larvae 

 of underwoodi, so we know nothing of their habits. 



The habit of dwelling in and around waterfalls and cas- 

 cades does not appear to have been mentioned for any other 



