10 TIIE CANADIAN ENTOMOLOGIST. 



to the presence or absence of metathoracic thorns j and of my undescribed 



species but two belong to the latter category. In fact it would seem from the 



following table, that a thorned metathorax is rather a S. A. than a N. A. 



character. 



GENUS HEMITELES. 



Group A. : — Two thorns more or less distinct, one on each side of the metatho- 

 rax, and directed hackwards and outwards. H. tricolor, Brulle, Brazil. H. 

 fasciipennis, Br., Brazil. H. xanthogaster, Br., Brazil. H. rujiventris, Br., S. 

 Am. H. striatus, Br., Columbia. H. lepidus, Br., Brazil. H. pulchellus, Br., 

 Brazil. H. fuscipennis, Br., Hayti. H. incertus, Cresson, Cuba, and two unde- 

 scribed species from Illinois, U. S. In all 7 S. A., 4 N. A. sp. 



Group B. : — Metathorax unarmed. In all 13 N. A. sp., and none at all from 

 S. A. 



a. Wings not handed loith fuscous. H. amcenus, Cress., Cuba. H. hicinctus, 

 Cress., Cuba. R. subflavescens, Cress., Cuba. 3. [Oryptus] orous, Say., and 

 six undescribed species from Illinois, U. S.* 



o. Wings with one fuscous hand. One undescribed species from Illinois, U. S. 



c. Wings with two fuscous hands. H. \Cryptus\ tenellus, Say., Penna., U. S. 

 H. thoracicus, Cresson, Cuba. H. nemativorus, n. sp. 



Through the kindness of the Editor, my cabinet has been enriched by a 

 fine 9 specimen of IT. nemativorus, of which I had previously possessed but 

 three £ , captured at large in Illinois. His account of its larval and pupal 

 history is as follows: "On June 29th I observed to my surprise a Saw-fly 

 cocoon (Nematus ventricosus, Klug.) attached to a leaf high up on a goose- 

 berry bush, instead of on or under the surface of the ground as usual. 

 Thinking that the unwonted situation might be the effect of a parasitic attack 

 upon the larva, I brought the specimen in, and a few days afterwards found 

 that there had emerged from it the Hymenopteron that I now send you ! " 

 Now, as I know that this very same species of Hemiteles occurs near Rock 

 Island, in Illinois, where as yet Nematus ventricosus has not been introduced, 

 it follows that it could not have been imported from Europe along with this 

 pestilent Saw-fly, but must be in all probability an indigenous species. Hence 

 we may draw the further conclusion, that a native American parasite can and 

 sometimes does acquire the habit of preying upon a vegetable-feeding insect 

 imported among us from Europe. The same conclusion, indeed, follows 



*In 18<30 and 1861, as I have stated in a paper on the Injurious Insects of Illinois 

 (Trans. 111. St. Agr. Soc. IV., p. 369), I bred from 50 to 70 £ £ individuals of an 

 undescribed Pezomac/tus (P. Heteropterus, Walsh, MS.), a genus which is normally 

 aptersqs and has an aborted thorax like that of a worker ant. Out of this large num- 

 ber there were produced four males, which had the complete wings of a Hemiteles, and 

 all the other characters of that genus, including of course the fully-developed thorax. 

 Hence I infer that a Pezomachus is nothing but a degraded Hemiteles. I may add that 

 this species — as well as two other Pezomachus in my collection, including P. minimus, 

 Walsh — had no metathoracic thorns, and that the winged % % , belonged to B. a of 

 this table. 



