1899 ] NATURAL SCIENCES OF PHILADELPHIA. 253 



Pseudomaeromia aud Zijgomjx, genera confined to the Old World, it 

 is evident that in spite of the resemblance in many peculiarities, no 

 com])lete parallelisms in structure exist. Thus Macrothemis, the most 

 specialized of the former group, agrees with Zygonyx ida in charac- 

 ters numbered 3, 6, 9, 12 and 13, but differs from Z. ida in Nos. 

 2, 10, 14 and 15; it agrees with Pseudomaeromia speciosa (pre- 

 tiosa 9 ) in Nos. 2, 3, 6 and 1 4, but differs therefrom in Nos. 9, 

 10, 12 and 13; it agrees with Ps. hova in Nos. 3, 6, 10 and 14, 

 but differs therefrom in Nos. 2, 9 and 12. Similar results follow a 

 comparison of the other genera. 



Dr. Karsch" has pointed out a fui'ther analogy between Pseudo- 

 maeromia and Macrothemis : the females have a strong tendency to 

 colored wings, the males to hyahne wings, although in the Libel- 

 lulinse, as in other insects, it is usually the reverse. 



As regards climatic distribution, both the American and the Old 

 World genera are inhabitants of the tropical and subtropical zones, 

 the northern and the .southern boundaries of the latter being formed 

 by the annual isotherms of 20° C. The one exception to this state- 

 ment appears to be a male from Chile, referred to variety typographa 

 of Macrothemis inequiunguis.'' 



I believe that we do not yet know enough of the relationships 

 of the Libellulinse to enable one to form an opinion on this ques- 

 tion : Have the peculiar forms of the tarsal nails and of the femoral 

 armatures been independently acquired by these New World and 

 these Old World genera, or are they inheritances from a common 

 ancestor ? Of the physiological significance of these structures we 

 know absolutely nothing, and we await the observations of some 

 naturalist on the living insects to supply us with such information. 



« Ent. Nach., xvii, p. 73, 1891. 



' Proc Bost. Soc. Nat. Hist., xxviii, p. 319. 



