2 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 82 



effort has been made to use in the keys and descriptions characters 

 which it is hoped will clearly distinguish the species included in 

 the paper. It must not be supposed that the tyro will be able at 

 once to determine species with these data in hand, as the insects are 

 not at all easy to determine, but with the aid of the figures and 

 careful descriptions of the various structures of the species pre- 

 sented herein it is we hope a possibility for any capable hymenop- 

 terist to establish definitely the identity of the included species. 



I find in this group, as I previously discovered in Tiphiinae, a 

 great similarity in the hypopygia of closely allied species, and con- 

 sequently I have made but little use of these organs in distinguishing 

 species. It may be noted, however, that there are several species 

 in which the hypopygia are quite distinctive, that the ultimate and 

 penultimate segments show more appreciable distinctions for the 

 differentiation of species, and that the ultimate segment in Dio- 

 dontus and Psen has a longer, more curved, and much sharper 

 pointed apical process than does Psenia. In Psen the process is very 

 acute, bare at apex, and stinglike, while in Psenia it is flat, rounded 

 at tip, and furnished with microscopic hairs, the longer of which 

 are at the tip. 



There are characteristic features in the anal lobe of the hind 

 wing of the various genera, but I have not made use of these in 

 my keys, as there is difficulty in determining the exact form of 

 the lobe in most specimens in collections because of the folding or 

 warping of the wings. 



The wasps are solitary, making their nests in stems of plants, 

 in wood, or in the earth, and provisioning them with Hemiptera, 

 mostly small leaf-hoppers. The museum collection contains large 

 series of two species which were reared from cocoons found in the 

 earth, but there are no records of the food habits of the species on 

 the attached labels. Nothing is known of the parasites of the North 

 American species, nor in fact if there are any. 



KEY TO THE GENEKA OF PSENINAE 



1. Cubitus of hind wing with its base proximad of median transverse vein ; 



occipital carina connecting witli the carina surrounding moutli cavity con- 

 siderably distant from median line of venter of head Psen Latreille 



Cubitus of hind wing with its base distad of median transverse vein 2 



2. Occipital carina connecting with the carina surrounding the mouth cavity 



considerably distant from median line of venter of head ; face with a 

 prominent median carina, which lies between bases of antennae and con- 

 nects with a raised line which extends from each side of face below 



antennal bases _ Diodontus Curtis 



Occipital carina carried around back of head and not connected with the one 

 surrounding the mouth cavity, sometimes rather widely separated from 

 the latter on median line of venter of head ; face without a prominent 

 carina as above, and lacking lateral transverse raised lines. 



Psenia, new genus 



