(JOS [December 



and inquilinous, like the othei* larva, iu the gall where it occurred. 



I have noticed towards the last of August galls about the size of the 

 head of a large pin. similar to S. semen, and often similarly confluent, 

 o'rowino- in con.siderable abundance on the leaves of the River Kirch 

 (Betula nigra), chiefly or almost entirely on their upper surface. And 

 on the leaves of the Button-bush (Cephalanthus) I have noticed at the 

 same period of the year galls of the same character, in the same luxu- 

 riant profusion as S. semen occurs on the Black Willow, whole bushes 

 being covered with them ; but in neither of the two kinds could I dis- 

 cover any larvae. I believe them both to be the work of Cieidomijla. 

 It does not follow, because all these galls are so small, that therefore 

 their Gall-gnats must be abnormally small. The gall S. rhodoi'.des n. 

 sp. is about 4 times as long and wide as the Grail *S'. gnaphalioides n. sp., 

 yet the Gall-gnat produced from the latter is only \ shorter than the 

 (rail-gnat produced from the former. 



Larva, pupa and imago unknown. 



No. 15. Gall S. aenigma. n. sp. — On S. nigra. A polythalamous, crumpled, ir- 

 regularly sjilierical or ellipsoidal mass, something like the aborted mass of 

 flower-buds of a common cauliflower, but with a more ragged and uneven sur- 

 face, .30 — 1.10 inch in diameter, and growing almost sessile or sometimes on a 

 stem as long as .50 inch, which is often branched and much flattened or dis- 

 torted, from the side or occasionally from the tip of twigs .05 — ..30 inch in dia- 

 meter. When cut into early in the summer, there is seen to be no regular heart 

 or symmetrical arrangement of the parts, as there is in all monothalamous galls, 

 and the stem is crisp and rather fleshy than woody. This gall first appears 

 early in June, being chiefly a deformation of the flower-catkins, but occasion- 

 ally, unless I was deceived from confounding it with S. semen n. sp., which I 

 think must have been the case, of the leaves. At that time, and for a month 

 or two afterwards, it is of a pale green, but long before autumn it dries up and 

 becomes brittle and of a dark ash-gray color, without, however, losing its origi- 

 nal shape, and hangs on the trees till long after the next spring opens. It con- 

 tains, so far as I could discover, no regular cells, but the larvae of the Gall-gnat 

 appear to burrow irregularly in the main stem and its branches. On the same 

 twig may often be seen 6 or 8 of these galls at irregular intervals of half an inch 

 or U inches, and frequently two of them grow side by side and run together. 

 "Whole trees are sometimes so covered by them, that the galls seem almost half 

 as numerous as the leaves. As usual, the twigs, unless very large, are killed by 

 the presence of these galls shortly after the galls have become mature. De- 

 scribed from 150 — 200 specimens. Very common and abundant everywhere in 

 Rock Island County, Illinois. 



Larva. — On June 19 the larva, or what I took to be the larva, of 

 the gall-maker was small and barely visible iu the stem of the gall, but 



