452 A YEAR OF COSTA RICAN NATURAL HISTORY 



of the midrib opposite or just below the bases of each pair 

 of leaflets. Both kinds produce the yellow fruit bodies at 

 the tips of the pinnules of the young leaflets, and both may 

 be inhabited either by black or by red ants. Our Santa 

 Cruz specimens have been identified by Professor Wheeler 

 as Pseudomyrma belli, Ps. nigrocincta and Ps. ?iigropilosa 

 (larger than nigrocincta, reddish with black hairs especially 

 near the hind end, facultative). The second species of 

 Acacia mentioned sometimes had the thorns abnormally 

 enlarged so as to be four or more inches in length and half 

 an inch or more in diameter except at the free end, where 

 the tip of the thorn retained its usual dimensions. The 

 enlargements like the unmodified thorns were hollow but I 

 do not know their significance; they were not found on all 

 plants.' The popular name of the bull's horn thorn is "cuer- 

 nezuelo." On several occasions I saw empty birds' nests 

 lodged within these spiny plants, although never the birds 

 which had built them. Seiior Bonilla said that the birds 

 choose such locations in order that the thorns may serve as a 

 defense against owls and hawks. How the nest-builders and 

 their young defend themselves from the ants I do not know. 



Another location for birds' nests which we saw near Santa 

 Cruz was the abandoned nests of termites, into which the 

 green parrakeets had made a hole, or, in one case at least, 

 a tunnel open at both ends. 



As we returned to Santa Cruz from the Pilas, crossing the 

 Diria at another point, we passed a swarm of Phalangids 

 similar to that described for January 21 but smaller; this 

 swarm was very close to the river bank. 



The Commission, having been invited to call on Seiior 



' I have allowed these notes on the Acacias to stand as written when the observa- 

 tions were made, adding the botanical names later. It seems possible that the 

 plants near Santa Cruz with "the thorns abnormally enlarged" may really have 

 been Acacia hindsii. I have no specimens which will determine the point. 



