OF WASHINGTON. 15 



of similar or homologous structures in other families, which are 

 of considerable importance in separating the species, as, for in 

 stance, the genus Macrocentrus, in which he finds a peculiar plate 

 on the femora, having one or more peculiar spines at the base, 

 which varies in different species. He believed, also, that the ar 

 rangement of the spines on the tibiag in other Hymenoptera, as 

 Ichneumonidae, etc., will be found of importance in the separation 

 of species. Mr. Schwarz said that these peculiar spiny structures 

 reminded him very forcibly of similar features in the hind tibias 

 and tarsi of Mordellistena, which are referred to in the writings 

 of LeConte and Smith as ridges, and by European authors as 

 incisions. These furnish the only characters which can be used 

 in the satisfactory identification of species. They occur in both 

 sexes, and are usually found covered with pollen, the beetles being 

 of a flower-frequenting habit, and these spines are, therefore, 

 doubtless of importance as a means of cross-fertilization of plants. 

 Mr. Howard stated as a curious coincidence that the Elasminae 

 bear a close general resemblance to Mordellistena. 



Mr. Schwarz presented the following paper, illustrating it 

 with specimens and figures : i 



A "PARASITIC" SCOLYTID. 

 By E. A. SCHWARZ. 



Parasitism, as defined by Prof. Riley in a presidential address 

 recently read before our Society, cannot possibly occur in truly 

 phytophagous insects ; but if we take the term in its widest 

 meaning, as lately discussed by Dr. Stiles and others (see p. i), 

 we find in the life-histories of phytophagous insects various 

 phenomena which more or less closely approach. parasitism. 



Confining myself to the three great phytophagous families of 

 Coleoptera, I do not recall any instances of this sort among the 

 Cerambycidae and Chrysomelidae, but quite a number are known 

 among the Rhynchophora. Thus the larvae of Copturus 

 longulus inhabit the galls of Podapion gallicola, but they are 

 mere messmates, and their presence is not detrimental to the 

 welfare of the author of the gall. Some of our species of 

 Otidocephalus which have frequently been bred from various 

 Cynipid galls appear to have a similar mode of life. The larva 

 of Conotrachelus posticatus is known to live within certain 

 Phylloxera galls on Hickory leaves, and in this case the 

 Phylloxeras always perish, probably from starvation, since it can 

 hardly be assumed that the Conotrachelus larva is insectivorous. 



