474 PROCEEDINGS OF THE ACADEMY OP [Oct., 



to the south of Mexico, thence continued as a chain of ''islands" in 

 the midst of lower and hotter lands. Considering the zones of mean 

 annual temperature in order, from the hottest to the coldest : 



Zone I (more than 30° C. = 86° F.) is doubtful, as stated in the 

 explanation of the map; no species of Odonata are known to be 

 restricted to the area supposed to constitute it. 



Zone II (30°-25° C, 86°-77° F.) is continuous on the Atlantic, and 

 also on the Pacific slope, for the entire length of its extent, from about 

 20° north latitude on the eastern, or 25° north on the western, coast 

 of Mexico to South America. The Atlantic and Pacific belts of this 

 zone are connected at the Nicaraguan lakes and at the Isthmus of 

 Panama. This zone therefore offers a pathway for the extension, 

 northward or southward, of species which find in it temperature con- 

 ditions similar to those which prevail over large areas of South Amer- 

 ica.^® It actually possesses a larger nimiber (91) of species also found 

 in South America than any other zone, although Zone III has 90 

 such species. Zones II and III have respectively 48 and 47 species 

 also found in the West Indies, larger numbers than for the other zones. 

 Peculiarities of Zone II are Perilestes (Costa Rica), Argiallagma (Guate- 

 mala), Telebasis 4 species, M etaleptohasis , Neoneura, Protoneura 5 

 species, NephepeUia and Rhodopygia, all genera found in South America 

 and the West Indies. Yucatan, Campeche and most of British 

 Honduras lie within this zone, and these three have no endemic species. 



Zone III (25°-20° C, 77°-68° F.), the Mexican Tierra Caliente of 

 Hann,^° extends continuously southward from the Gulf States on the 

 east, and from Arizona and California on the west, to southern Nica- 

 ragua, where it is interrupted by Zone II. The Atlantic and Pacific 

 belts are confluent from the southern part of the State of Puebla to 

 the western part of Chiapas, and again for the southern part of Hon- 

 duras and most of Nicaragua. After its interruption in southern 

 Nicaragua, this zone reappears in northwestern Costa Rica and extends 

 almost to the Isthmus of Panama. Zones III and IV possess an equal 

 number (27) of species also found in Northern America, a larger num- 

 ber than for the other zones. Characteristic for this zone are Philo- 

 genia (not north of Costa Rica), Palcemnema, Progomphus 3 species, 

 Epigomphus 4 species, genera chiefly South American in their dis- 

 tribution. 



'* The distribution of the Odonata by temperature zones in South America 

 should also be considered here, but even the first steps in investigating the South 

 American Odonata from this point of view have vet to be taken. 



^^Handbuch der Klimatologie, 2te Aufgabe, Bd.'ll, p. 285, Stuttgart, 1897. 



