Kinsey: Studies of Cyni/pidse 



105 



Kieffer states in Das Tierreich that Plagiotrichus kief- 

 ferianus is the agamic generation of P. ilicis. I have not seen 

 a further account of this hfe history, and I do not know of 

 any other Hfe history being proved in the genus. But this 

 alternation is entirely probable because the galls of the two 

 generations are fundamentally alike, differing only in con- 

 nection with their occurrence on different parts of the hosts, 

 and the bisexual and agamic insects clearly belong to the same 

 genus. All of our American bisexual species occur in galls 

 which are typical of ilicis, and all of our agamic species occur 

 in galls similar to kiefferianus. Probably both generations 

 have been described as separate species for some of our east- 

 ern American insects of this genus. On the Pacific Coast 

 apparently only one bisexual form, P. congregatus, is de- 

 scribed, altho 1 have the galls of several forms which very 

 probably alternate with varieties of P. chrysolepidicola, P. 

 suttonii, P. perdens, or P. asymmetricus. Several of these 

 undescribed galls are leaf vein swellings little different from 

 ilicis galls. Some are more woody petiole swellings. 



A fact to be emphasized is the close similarity of the two 

 generations, except that one is agamic and the other bisexual. 

 My detailed description of the insects and galls fits both the 

 bisexual and agamic forms of all the species yet known. Again 

 we find that alternation of generations is only an extreme 

 development of seasonal dimorphism. 



In addition to the species treated in this paper, the follow- 

 ing American Cynipidss should be assigned to Plagiotrichus: 



Plagiotrichus concolorans (Kinsey) {= P. cicatrictdus 

 (Bassett)?). Agamic; eastern; white oaks. 



P. congregattis (Ashmead). Described from female only; 

 both sexes among the types; Pacific Coast; on white oaks. 



P. cornigerus (Osten Sacken). Agamic; eastern; on 

 black oaks. 



P. punctatus (Bassett). Agamic; eastern; on black oaks. 

 P. quinqueseptum (Ashmead). Agamic; eastern; white 

 Oaks. 



P. reticidatus (Bassett). Only female described; south- 

 western ; white oaks. 



P. scitidus (Bassett). Bisexual; eastern; on black oaks. 



P. tuniificus (Osten Sacken). Bisexual; eastern; on black 

 oaks. 



