1908. 



NATURAL SCIENCES OF PHILADELPHIA. 



473 



Table S. — Number of Species, etc., of Odonata Recorded from the 

 Departments of Costa Rica, and of the Localities 



AT WHICH they WERE COLLECTED. 



(See the explanation in the text.) 



Total number of species, etc., Pacific slope '. 67 



Total number of species, etc., Atlantic slope 59 



Total number of species, etc., common to Pacific and Atlantic slopes 28 



Although writers on other groups in the Biologia have distinguished 

 between a "North" and a "South Mexico," the division hne being near 

 the Tropic of Cancer, the data at hand for the Odonata do not seem 

 to indicate any such distinction. 



Relations of the Odonate Fauna to Teaiperature.^' 



In Plate XXVI we have given a map of the distribution of mean an- 

 nual temperatures in Mexico and Central America.^^ The topograph}^, 

 presenting a high paramesial axis running northwest and southeast 

 through the greater part of the district, has brought about the exist- 

 ence of parallel zones of temperature, decreasing in mean annual 

 intensity from each coast line to the axis. As a result the temperatures 

 are not distributed latitudinally, but a high cool tract extends far 



'' It is not intended that the remarks here made on the relations of Odonate 

 distribution to temperatvire, rainfall and other environmental factors are to be 

 interpreted as sho-\\ing the Hmits wliich these factors set to the distribution of 

 the insects in question. Our knowledge of the areas occupied by the latter is 

 still too imperfect to permit this. We may be said to know where many species 

 occur, but not where they do not occur. 



1^ Mr. C. H. T. Townsend, in his papers "On the Biogeography of Mexico, 

 Texas," etc. (Trans. Texas Acad. Sci., Vols. I and II, 1895 and 1897), has 

 laid great emphasis on the difference between apparent and sensible tempera- 

 tures, as obtained from dry and wet bulb thermometers respectively, liolding 

 that only sensible temperatures can be used in biogeographical work (I.e., 1, 

 pp. 89-90; II, pp. 65-67). .\s very few wet Ijulb readings exist for our dis- 

 trict, our data are those of his "apparent" temperatures only. I am indebted 

 to Dr. C. C. Adams for calKng my attention to these two papers, which seem 

 to have been omitted from the "Zoological Record." 



