106 



Indiana University Studies 



I shall withhold opinion on the generic position of some 

 other American Cynipidse from stem and leaf vein galls until 

 further revision of cynipid genera may indicate the several 

 trends of evolution. 



With many if not all of the species of this genus, each 

 variety is confined to a single oak. The influences of host 

 isolation have been greater than with some other Cynipidse, 

 and with some of the insects of the genus host isolation has 

 succeeded in developing more distinct varieties than geo- 

 graphic isolation has effected. 



Plagiotrichus asymmetricus, new species 



FEMALE. — Shows the following characters in addition to those com- 

 mon to ail species of the genus : Color light rufous brown and darker 

 to black; widened but not greatly so behind the eyes; antennae brown, 

 first four or five segments lighter, with 14 segments; mesonotum more 

 or less smooth and shining, but coriaceous in places, mol'e or less dis- 

 tinct; rugous striae radiating from the midpoint of the posterior margin, 

 anteriorly m_ore coriaceous or rugose; the thorax naked of hairs; parap- 

 sidal grooves never traceable for more than a short distance from the 

 scutellum, converging considerably posteriorly; median groove and an- 

 terior parallel lines barely indicated as marks, not as grooves or lines; 

 lateral lines short, oval depressions; a smooth, arcuate foveal furrow 

 hardly divided into two by a very fine, median ridge; mesopleurae brown- 

 ish rufous or darker, at least in part aciculate; abdomen rich rufous 

 brown or darker, entirely smooth, shining, neither punctate nor reticu- 

 late, about as high as long, the second segment occupying hardly half the 

 area; legs largely rufous, hind tibiae darker centrally; areolet of mod- 

 erate size to very large; cubitus not reaching the basalis; length 1.7- 

 3.0 mm. 



GALL. — Stem swelling containing compact clusters of larval cells. 

 Polythalamous. The swelling covered with bark normal in appearance; 

 a gradual enlargement, often asymmetrical on the stem; up to 30. mm. 

 long, by 20. mm. broad. Internally, the larval cells in compact masses, 

 each cell with a distinct and sometimes separable lining, not very thin 

 walled; the cells usually densely clustered. On young stems of Quercus 

 chrysolejyis. 



RANGE. — California: Pasadena and San Bernardino to Dunsmuir 

 and Ukiah. Probably wherever Q. clirijsolepis occurs. 



The gall of this species does not differ materially in ex- 

 ternal appearance from the galls of two other Pacific Coast 

 species found on the same host : Andrictis spectabilis Kinsey 

 SiTid Plagiotrichus chrijsolejMicola (Ashmead). 



The species presents the typical condition of distinct vari- 

 eties wherever it occurs in a distinct faunal area. Between 



