460 A YEAR OF COSTA RICAN NATURAL HISTORY 



from Nicaragua, and the South American examples men- 

 tioned in literature up to that time were very few in number. 

 It was interesting to learn that these rare little dragonflies 

 are inhabitants of dry forests such as this — no information 

 of a definite character being hitherto at hand on this point. 

 The male of this species is most curious in possessing two 

 slender horns each 1.18 mm. long, on the forw'ard upper sur- 

 face of its mesothorax and directed upward and forward 

 and curved toward each at their sharply-pointed tips. Their 

 relatively great length is only appreciated when it is known 

 that the greatest height of the thorax at any point is but 

 2.16 mm. I am sorry to be unable to record any observa- 

 tions upon this insect while alive which would give some 

 clue as to the function of these peculiar, and, for males, rare 

 structures. The females have, in the place of these horns, 

 two conical tubercles each .11 mm. in height. The total 

 length of the body in both sexes is one and three-quarters 

 inches, the wing-spread about the same. The thorax is 

 yellowish-green in life with a mid-dorsal dark metallic green 

 stripe. 



We had some excellent views of monkeys in this forest; I 

 heard the howling of the congos many times in the distance 

 at Santa Cruz as well as on our journey thither, and this 

 morning we heard them frequently from the first moment 

 we entered the forest. At last we were so fortunate as to 

 meet a troop of eight or nine in the trees immediately over 

 and alongside of the road and not too high to be seen dis- 

 tinctly. The Congo {Alouatta villosa) is the largest of the 

 Costa Rican monkeys and is entirely black, the males with a 

 heavy black beard. This troop included individuals of 

 difi"erent ages and sizes. They showed no special signs of 

 fear at our presence. We stood beneath them and called to 

 them in our deepest tones, some of the congos replying in a 

 roar not unlike a lion's. 



