Co7'relation of Structure and Host- Relation 179 



basis for the first of the prerequisites — that of systematic classi- 

 fication from structure alone. 



For the second, knowledge of host-relations, we have 

 Mayr's table and the extensive rearings and notes of the Divi- 

 sion of Entomology of the U. S. Department of Agriculture, 

 which my chief, Dr. C. V. Riley, permits me to use for this 

 purpose, as well as his own personal notes made mainly in 

 Missouri prior to 1876. In all these comprise more than 200 

 rearings and of the 150 species in the National Museum collec- 

 tion, about 120 have been reared and the host-insect identified 

 with sufiicient accuracy for our present purpose. 



L,et us see then how far uniformity of habit goes in this 

 group, by taking up one after another of the described genera : 



Rhopus Forster. — European : — Coccus racemosus. 

 American : — Pseudococcus aceris, (111.) Dactylopius ephedra (Cal.) 



Holcothorax Mayr. — Etiropean : — Ivithocolletis 5 spp., Tischeria com- 

 planella, Nepticula splendidissimella, Hyponomeuta 4 spp., Plusia 

 moneta. 



Aphycus Mayr. — European : — Coccidae 9 spp., nearly all LecaniinEe. 

 American : — Lecauium, 9 spp., (Mo., S. C, Ala., Cal., Va., Oreg. Fla.) 

 Dactylopius, 2 spp., (Cal.) Ceroplastes, 2 spp., (Ariz,, N. Mex.) 

 Kermes i sp., Pulvinaria iunumerabilis, (la.) Diaspis ros», (N. 

 J.) Mytilaspis citricola, (Fla. ) 



Blastothrix Mayr. — European : — Coccidte, 9 spp., mainly Lecaniinse. 

 Atnerican ; — I^ecanium, 4 spp., (N. Y., Cal., Fla.), Pseudococcus 

 yuccEe (Cal.) 



Psilophrys Mayr. — European : — I/Ccanium sp. 



Leptoniastix Fcerst. — American : — Dactylopius destructor, (D. C. ) 



Copidosoma Ratz. — Em-opean : — Agrotis fumosa, Hadena polyodon, Leu- 

 cania albipicta, Plusia 5 spp., Catocala electa, Geometra, Cidaria 

 variata, Eupithecia 4 spp., Tortrix sp., Carpocapsa splendora, Hy- 

 ponorueuta 2 spp., Cerostoma sp., Depressaria 2 spp., Gelechia fa- 

 vilaticella, Lita alsinella, Tachyptilia populella, Coleophora, 2 spp. 

 American : — Papilio turnus, (W. Va.) Celsena renigera, Plusia bras- 

 sies, (many states.) Aletia xylina, (Ark.) Acronycta sp., (Mo.) 

 Unknown Noctuid larvce, 3 spp., (Colo., Out., Quebec.) Sericoris 

 coruscaua, (N. H.) Gelechia gallffisolidaginis, (Mo. ) G. pseudaca- 

 ciella, (D. C.) G. gallteasterella, (N. J.) G.sp. (Ala.) G. viburnella, 

 (Mo.) G. epigseella, (Va.) Tinea grauella, (D. C.) Bucculatrix 

 thuiella, (Mo.) Coleophora sp., (D. C.) LithocoUetis fitchella, (D. 

 C.) Unknown Tineid larva, (Mo.) 



