190S.] 



NATURAL SCIENCES OF PHILADELPHIA. 



467 



Table 3. — The Relative Strength of the West Indian and South American 



Elements in Different Parts of the Odonate Fauna of 



Mexico and Central America. 



Area. 



Total number I Number of species, etc., 

 of species,! found also in the West 

 gtc 'j Indies, and their per- 



centage equivalents. 



Number of species, etc., 

 found also (outside of 

 Mexico and Cent. Amer.) 

 exclusively in S. Amer., 

 and their percentage 

 equivalents. 



Mexican plateau 81 



Mexico (asin Tables) 219 (221) 

 Yucatan and British 



Honduras 35? 



Guatemala and Hon-j 



duras I 161 (186) 



Costa Rica 101 (165) 



23 



49 (50) 



18? 



41 (50) 

 19 (45) 



28.4% 



22.4 (22.6) 



51.4 



25.5 (26.9) 

 18.8 (27.3) 



14 = 17.3% 



50 = 22.8 (22.6) 



8 = 22.8 



49 (61) = 30.4 (32.8) 

 37 (65) = 36.6 (39.4) 



(The parentheses have the same meaning as in Table 2, q. v.) 



or almost entirely {Argia), confined to the Americas. Lestes, Enal- 

 lagma, Ischnura, Mshna, LiheUula and Sympetrum are almost or quite 

 cosmopolitan, but are more abundant in the northern than in the 

 southern hemisphere. 



Of the seven endemic genera, Pseudostigma, Thaumatoneura and 

 Paraphlebia are South American in their affinities; the other four 

 are not so clear. 



Adding together the 9 species of these three genera, the 56 endemic 

 species of genera also occurring in South America but not in Northern 

 America (Table 4), and the 70 non-endemic species found elsewhere 

 exclusively in South America (Table 1), we have a total of 135 species, 

 or 46% of the fauna, as being of distinctly southern relationships. 

 Similarly, adding the 12 endemic species of genera also occurring in 

 Northern America, but not in South America (Table 4), to the 21 

 non-endemic species found elsewhere exclusively in Northern America 

 (Table 1) we have a total of 33 species, or 11% of the fauna, as being 

 of distinctly northern affiliations. 



In the endemic as well as in the non-endemic species, therefore, 

 the South American element^^ is much the strongest in Mexico and 

 Central America as a whole. 



"While the expression "South American element" has been used in these 

 pages to designate those species found at the present time in South America 

 also, there seems to be no evidence to decide whether such Odonata, or their 

 ancestors, entered Mexico and Central America from the south, or whether 

 South America received them from the former countries. Probably only further 

 discoveries of fossil Odonata will settle this question. 



