128 THE ENTOMOLOGIST. 



** The space between the antennae most frequently very wide; 



metathorax much shorter than high. - - Thersilochus. 



Head small ; wings sometimes without an areolet, transverse 



cubital nervure sometimes wanting ; areolet when present a 



transverse rhomboid. Plectiscus. 



[This genus, originally formed by Gravenhorst, contained 

 several small Ichneumons, which varied somewhat in important 

 particulars. Haliday made the genus Helictes from some of these 

 insects; and about the same time (1839) Schiodte described the 

 genus Megastylus, containing Haliday 's group of insects ; but as 

 Schiodte's paper was published a short time before the other it 

 obtained priority. Holmgren has placed this genus amongst the 

 Tryphonidae. Forster (Verb.. Nat. ver. preus. Rheinl. xxviii., 1871, 

 p. 71) has published an elaborate monograph of Plectiscus, elevating 

 the genus of Gravenhorst into a family, and dividing it into over 20 

 genera; and, as several of these have occurred in Britain, we have 

 added a short table of them as subgenera: — 



A. "Wings with an areolet. Plectiscus. 



B. Wings without an areolet. 



a. First joint of flagellum shorter than the second. 



Second joint of flagellum in the male notched. - Miomerus. 



b. First joint of flagellum as long as, or longer than, the second. 

 * Fifth to seventh joints of flagellum of male deeply notched. 



Idioxenus. 

 ** Fifth to seventh joints of flagellum of male not notched, 

 f Metauotum divided into two parts by a deep transverse 

 depression. ------- Dicolus. 



ff Metauotum not so divided ; back part of head with a transverse 



ridge ; stigma not narrow. 

 J Metathorax at the base not distinctly and regularly divided 

 into area? ; antenna? more than thirty joints ; abdomen 



depressed. Megastylus. 



H Metathorax without distinct area? at the base. 



The apical joint of tarsi not thickened; transverse anal 

 nervure distinctly interrupted ; the first division of the 

 radius interrupted, and with the second does not form 

 a sharp angle ; hind femora and tibiae not thickened. 



Proclitus.] 



Subdivision 2. — Hind femora armed with a spine in the middle beneath. 



Pristomerus. 



Division II. — Abdomen sessile or subsessile. 



A. All the tarsi slender. 



a. Claws of tarsi not pectinated. 



* Aculeus short. Exetastes. 



** Aculeus as long as the body. ----- Arotes. 



b. Claws of tarsi pectinated ; abdomen sessile. - - Banchus. 



B. Hind tarsi thickened ; claws pectinated. - - - Scolobates. 



