194 BRITISH ICHNEUMONS. [ Acrotomus 

The only genus of this group with the lower mandibular tooth dis- 
tinctly the longer, since in all the following genera it is of equal length 
with the upper. The species are found in woods, and oviposit in Hyme- 
nopterous larvae ; they are very nearly confined to the Paleaearctic region, 
as far as is at present known.* 
Table of Species. 
(4). 1. Antennae entirely black; clypeus 
apically rounded. 
(3). 2. Face and central segments entirely 
black ye ag fs ... Ts ALACER,-Graw; 
(2). 3. Face and apices of central segments 
broadly pale Na ae .. 2. RIDIBUNDUS, Grav. 
(1). 4. Antennae not entirely black ; clypeus 
) 
apically subtruncate. 
) . Nervellus intercepted below centre ; 
genal costa simple. 
(7). 6. Clypeus not transverse, apically sub- 
) 
) 
Lal 
emarginate .. - a 723. LUEIDULUS; Graz: 
(6). 7. Clypeus transverse, apically subro- 
tundate. 
(9). 8. Abdomen centrally rufescent ; cheeks 
buccate ts bi t oul #. EMPICERS Gran 
(8). 9. Abdomen not red-marked; cheeks 
not buccate. 
(11). 10. Face laterally pale; thorax immacu- 
IETS oe Ae ae ne 2+ 5. oSEXCINGLUS, Gratzer 
(10). 11. Face entirely pale ; thorax flavidous- 
marked = is * .. 6. SUCCINCTUS, Grav. 
(5). 12. Nervellus intercepted in centre ; 
cheeks dentate below... .. 7. MESOLEPTOIDES, Szeph. 
1. alacer, Grav. 
Tryphon alacer, Gr. 1.E. ii. 132; Ste. Ill. M. vii. 233, ¢. T. anceps, Ste. 
lib. cit. 243. Acrotomus xanthopus, Holmgr. Sv. Ak. Handl. 1855. p. 223; 
Brisch. Schr. Nat. Ges. Danz. 1878, p. 103, ¢. A. alacer, Pfank. Zeits. Hym. 
Dip. 1906, p, 86. 
A nitidulous black species. Head scarcely constricted posteriorly ; 
black with the palpi and mandibles except at their apices pale; clypeus 
slightly convex and apically rounded. Thorax stout with the apically 
flavidous scutellum elevated and the pleurae obsoletely punctate. Abdo- 
men narrow, somewhat longer than head and thorax, black with the anal 
segments apically pale; basal segment narrow and scarcely explanate 
apically; the second and third glabrous and convex, remainder sub- 
pubescent. Legs elongate and slender, rufescent with the posterior 

*ACROTOMUS LAETUS, Grav. 
Mesoleptus laetus, Gr. 1. E. ii. 50; Ste. Ill. M. vii. 219. Exenterus orbitatorius, Schiod. Guér. Mag. 
1839, p. 11, nota. Acrotomus orbitatorius, Brisch. Phys. Ges. Konig. 1871, p.97; Schr. Nat. Ges. Danz. 
1878, p. 103, ¢ 2; Voll. Pinac. pl. x], fig. 2. 
This is said by Pfankuch in 1906 to be the true synonymy of Mesoleptus laetus; but since it is 
known as British upon no higher authority than Stephens (1835) and has not since been noticed with 
us, we must regard his record from ‘‘ Coombe Wood in July” as extremely doubtful, till further 
evidence be forthcoming. Pfankuch adds that T. cephalotes, Grav., is synonymous with this 
species; but all the specimens so named in the National collection are referable to Cteniscus, having 
equal mandibles, ’ 
