No. 1*2.— The Odonate genus Macrothemis and its Allies . 
By Philip P. Calvert. 
With tivo plates. 
In the summer of 1897, by the kindness of Mr. Samuel Henshaw, 
of the Museum of Comparative Zoology, Cambridge, Mass., the writer 
spent some weeks in studying the extensive collection of Odonata of 
that institution. Part of the time was devoted to a comparison of 
material collected in Mexico with that possessed by the Museum, 
particularly in the genera Macrothemis and Brechmorhoga. This 
necessitated a study of all the species referable to these two groups, 
preliminary to satisfactory identifications. It seems worth while 
publishing the results of this study, with some additions based on 
the collections in Philadelphia, although the present paper is not to 
be regarded as even an attempt to monograph the genera in question. 
On the contrary, the aim is merely to define more precisely some 
forms hitherto known from very brief descriptions, to indicate the 
differences between such forms, as well as some of the variations 
which they show. It is hoped that these data will aid in clearing 
the way towards acquiring a better understanding of the relation¬ 
ships of these insects when more extensive material is available. 
The Common Characters of the Genera here treated. -The 
genera Dythemis, Paltothemis, Brechmorhoga, Scapanea, and 
Macrothemis, of the subfamily Libellulinae, agree in the following 
characteristics : — 
Eyes in contact for a distance less than the antero-posterior 
dimension of the occiput; hind lobe of the prothorax with its cen¬ 
tral portion produced backwards and narrower than the other lobes, 
its hind margin entire; no additional (or supplementary) transverse 
carina on the fourth abdominal segment; lower angle of the triangle 
of the front wings placed only slightly^ beyond (distad) the level 
of the outer angle of the triangle of the hind wings (i. e. not so 
far beyond as the length of the latter triangle); sectors of the 
arculus arising by a common stalk ; no supratriangulars (hyper- 
trigonals); last antenodal on the front wings not continued to the 
median vein; both sectors of the triangle, in the hind wings, 
arising from its hind (lower) angle; genital hamule of the males 
not bifid, more prominent than anterior lamina or genital lobe; 
