ART. 15«. REVISION OF SUBFAMILY PLATYGASTEEINAE FOUTS. 13 



VI. Genus TRICHACIS Foerster. 



Trichacis Foerster, Hym. Stud., Heft. 2, 1856, p. 115. Three species. Geno- 

 type. -Platygaster prsis Walker. (By original designation.) 



This is a genus occupying a position very similar to that formerly 

 held by Polygnotus. In other words it is separated from an allied 

 genus, Isocyhus, by characters which are relative and therefore impos- 

 sible to define exactly. It is too much to expect that the head in the 

 one group should always remain distinctly transverse and in the 

 other cubical. It is certain that species exist which serve to unite 

 the two. Indeed we have in Trichacis rvjipes a form which has the 

 head distinctly less than twice as wide as long, a condition approach- 

 ing that found in Isocyhus. 



Probably the best way to fix the position of Trichacis in mind 

 would be to remember that it has all the peculiarities of Platygaster 

 except the smooth scutellum with its scanty covering of hairs. 



Ashmead, in his monograph of the North American Proctotrypidae, 

 referred two species belonging to Trichacis to the genera Isorhombus 

 and Synopeas. The species, Isorhombus arizonensis Ashmead and 

 Synopeas cornicola Ashmead are redescribed below and should be 

 readily recognized if the description is properly used. 



TABLE TO SPECfES. 



1. Head less than twice as wide as long 1. rufipes Ashmead. 



Head two or more times wider than long 2. 



2. Occiput strongly transversely striate 2. rubicola Ashmead. 



Occiput not or very finely striate 3. 



3. Scutellum very high, conical seen from the side, without a distinct tuft of hair 



at summit 3. arizonensis (Ashmead) . 



Scutellum low, not conical, with a distinct tuft of hair at summit 4. 



4. Abdomen in female less than twice as long as wide 4. cornicola ( Ashmead) . 



Abdomen in female twice as long as wide 5. virginiensis Ashmead. 



1. TRICHACIS RUFIPES Ashmead. 



Trichacis rufipes Ashmead, Bull. 45, U. S. Nat. Mus., 1893, p. 295.— Brues, 

 Bull. 22, Conn. Geol. Nat. Hist. Survey, 1916 (1917), p. 534. 



Female. — Length 2.20 mm. Head three-fifths as wide as long, not 

 emarginate posteriorly, wider than the thorax; occiput polished, 

 separated from the vertex by a low but sharp carina ; cheeks sha- 

 greened; interocellar space polished, shagreened laterally; frons 

 polished, narrowly shagreened laterally, with a few striae above the 

 antennae; pedicel twice as long as wide, as long and as wide as joint 

 three, a little longer and narrower than four; five triangular, as long 

 as four, as long as six but somewhat narrower; six as wide as long, 

 narrowed basally, a little longer than seven; seven to nine a little 

 wider than long; ten less than twice as long as wide, a little longer 

 than the pedicel, subacute apioally; thorax four-sevenths times as 

 wide as long, higher than wide; pronotum pubescent, polished; meso- 



