S nodulus, n. sp.
On S longifolia [interior]
A small, monothalamous, woody gall, sometimes terminal but generally not so, scarcely ever including any buds, growing on twigs .05^.15 inch in diameter, variable in shape, but generally consisting of a mere oval enlargement of the twig to half as large as its normal size for the length of .20 — .50 inch. The surface of the enlargement is either the usual color of the bark, or simply discolored and dark, or a little roughened with brown scales and longitudinally sinuate and interlacing stria. Occasionally it assumes the form of an elongate, lateral, bunnion-like swelling about .27 inch long and .1.3 inch wide, as in some varieties of S. batatas n, sp., and in one specimen there occurred an intermediate grade between this variety and the normal type; occasionally it grows at the base of a very small side- shoot, when the tip of the side-shoot shrivels up and perishes ; and occasion- ally the growth of the side-shoot is completely arrested, and the gall becomes a mere obhemispherical swelling about .20 inch in diameter, with its upper sur- face in an irregular plane, and very rugose and brown, located at the spot where normally there ought to be a bud. On cutting into this gall in Novem- ber, it is found to contain a single cell — smooth on the inside when the gall- making larva is present, but, as in ^S". batatas, without any separate cocoon — and much reddish-brown matter where the larva had formerly burrowed, and occa- sionally some grass-green soft matter: but the external walls are still in their normal white, ligneous state, the larva having apparently confined itself to the pith and the wood immediately surrounding the pith. Described from 9 specimens. Rare uear Rock Island. Externally this gall cannot be distinguished from the smaller varieties of C. bata- tas, but the former is monothalamous, the latter polythalamous ; neither can it be distinguished, except by its much smaller size and its much smaller cell, from the Tenthredinidous gall G. nodus which grows on the same willow. Of the 9 galls examined, 7 were unbored, 3 of which contained each a single larva of Oec. s. nodulus, 1 a single hairy Chalcididous larva, probably a Callimome, 1 a single Curculionidous larva, no doubt an Inquiline. and in 2 the gall-making larva was absent and must have perished in early life, for although its work was plainly visible yet the gall was not bored. In none of the 9, whether bored or un- bored, had the twig been killed, except in the very small gall before referred to, where the terminal bud had sprouted out into a minute shoot which afterwards perished. The smallness of this larva and there being only one in each gall, readily account for this otherwise anoma- lous fact. I found Dec. 1st in one of these galls, which had been bored by a single hole and contained no Cecidomyidous larva, a minute Lepidop- terous larva, doubtless an inquiline, and over a dozen small and young Aphis, which had probably taken refuge there for the winter. May not Hartig have been deceived by some such case as this into suppos-ing, that certain European Willow-galls were the work of Aphis ? (See above, p. 551.) On July 31st I found a bored and empty specimen of the Tenthredinidous gall C. pomum tenanted in the same manner by over a dozen Aphis.
