60 Journal New York Entomological Society. t^oi. XX. 



different lots of perfectly fresh twigs of Ptelea trifoliata. He says 

 in his notes : " The branch with the Enchenopa which I sent you is of 

 the hop-tree {Ptelea trifoliata). The insects have, during the past 

 two summers, been quite numerous in Jackson Park, Chicago, but I 

 have not found them on any other shrub or tree." In the first lot 

 received, I could find no eggs for some reason, the frothy masses 

 appearing to have deteriorated. They were dirty, dry and brittle, 

 but under the microscope showed numerous nymphs, which, as I 

 stated later, were in the first stage. They were so small (between 

 1-1.3 mm.) that I was unable to see them with the unaided eye. I was 

 not sure whether they really came from the supposed egg-masses in 

 the above-mentioned condition. I then split one of the twigs, and 

 taking oft' the bark, found on its inner side the empty egg-shells, with 

 a few entire eggs. This proved that what I had erroneously taken for 

 egg-masses were merely masses of a substance heaped over slits on 

 the bark, somewhat in form of Qgg clusters, for a protective purpose. 

 The eggs are really laid in two rather parallel slits which are made 

 in the bark, side by side, in more or less obliquely arranged rows, as 

 shown in Fig. 3, which represents the inner side of the bark. The 

 frothy masses, if protected from wind and weather, however, seem 

 to persist for some time, as I have observed in specimens of twigs 

 kept in my collection for the past four years. I found considerable vari- 

 ations in the insects, taken from different plants, not only in the color 

 of the nymphs, but also in the form of the egg-mass, number of eggs, 

 and in the forms of the protecting masses. On Viburnum and Robinia 

 the egg-groups are more numerous and always laid in one direction, 

 as they rest mostly with the head directed upward and outward, in 

 crowded conditions, as shown in the bark of Ptelea in Fig. 3, where 

 one of the groups had been placed in the opposite position. But this 

 does not seem to be the case where the insects occur in smaller num- 

 bers, since it has not been found on both the plants observed by 

 myself. On Viburnum I found that they often prefer to begin on the 

 forkings of the twigs; on Robinia above the bases of the leaves or 

 thorns as shown in Fig. 4. In 10 specimens of covered egg-groups on 

 Viburnum, I found the number of eggs in a group ranging from 9 to 

 17; on Robinia, by inspecting 4 specimens, from 11 to 16, placed 

 rather irregularly in the slits, as one of them contained 10, the other of 

 the same group only 4 eggs. On the thicker twigs of Viburnum the 



