478 PROCEEDINGS OF THE NATIONAL MUSEUM vol. no 



presumably disc-shaped with an unsclerotized circumference; the 

 spiracle has an oval atrium and the closing apparatus, which has thin 

 walls, adjoins the atrium in some genera but not in others; the closing 

 apparatus has a length equal to five to seven times the depth of 

 the atrium; the skin is very smooth and appears to lack setae and 

 projections. 



Larval Key 



1. Lateral parts of labial sclerite produced into relatively sharp angles and not 



rounded Syrphoctomis 



Lateral parts of labial sclerite less sharp and more rounded 2 



2. Labial palps lobed Promethus ^ 



Labial palps oval 3 



3. Length of labial spine approximately equal to depth of main ventral part of 



labial sclerite Biplazon 



Length of labial spine shorter than depth of main ventral part of labial sclerite. 



Zootrephus 



The following are figured in the literature: Diplazon Jissorius 

 (Gravenhorst) (Schneider, 1950), D. laetatorius (Fabricius) (Scott, 

 1939), D. tetragonus (Thunberg) (Beirne, 1941), Promethus monticola 

 (Vollenhoven) (Scott, 1939), Syrphoctonus signatus (Gravenhorst) 

 (Scott, 1939), S. tarsaiorius (Panzer) (Scott, 1939; Beirne, 1941). 



The figiu-es of Scott are particularly good. Schneider figures 

 a labral sclerite in Diplazon Jissorius (Gravenhorst). This has not 

 been seen in any specimen of Diplazon examined in the present study 

 and neither Scott nor Beirne figure this structure. 



Subfamily Metopiinae 



Figures 48, 49 



Members of this subfamily are endoparasitic in Lepidoptera. The 

 parasites emerge from the pupae of the hosts. 



The epistoma is well sclerotized except in Triclistus; the pleurostoma 

 and hypostoma are well sclerotized; the hypostomal spur is absent 

 and the stipital sclerite extends dorsally to meet the hypostoma; the 

 labial sclerite is incomplete ventrally; on each maxUlary and labial 

 palp there is one large sensillum and one or several smaller sensilla; 

 the silk press is well sclerotized; there is a lightly sclerotized plate 

 ventral to the press containing two sensilla; this plate may represent 

 the dorsal part of the prelabial sclerite but is more probably the 

 ventral part of the silk press; the labral sclerite is absent; the mandibles 

 are relatively large and do not have teeth on the blade ; the antenna is 

 disc-shaped; the atrium of the spiracle is shallow; the closing apparatus 

 of the spiracle is thin-walled and with a length approximately equal 



2'Of Scott (1939). 



