Page:New Pacific Coast Cynipidæ (Hymenoptera).pdf/3

 in many minute details of venation, thoracic sculpture, abdominal and antennal characters; in atrimentus the parapsides are more convergent at the scutellum, the scutellum is less elongate, less rugose, with the foveal groove smoother and less distinctly bifoveate than in palustris. In the male of atrimentus the abdomen is not as small as in palustris. Atrimentus occurs on a white oak in one distinct faunal area; palustris on black oaks in a very different faunal area. It is exceedingly significant that the galls of the two species show similarity of structure, for as has been repeatedly shown the gall is an expression of the physiological nature of the insect. Physiologically then the two species are related, just as they are morphologically, but physiologically they differ even more markedly than morphologically. For though the galls are similar hollow bladders in the leaf, the Pacific Coast species does not have the thick and succulent walls of palustris; while the attached larval cell of atrimentus is distinctly unlike the remarkable, loose cell of palustris. Both forms are bisexual generations, developing very quickly in early spring on the unfolding leaves. The other generation of palustris, namely Andricus palustris form compressus (Gillette), is a wingless, agamic species forming a small, hollow, egg-shaped, separable gall on the leaves in late summer, the gall dropping to the ground in autumn, the insect emerging very early in the spring. It is not unlikely that atrimentus has a similar history, but it will be important that some one determine exactly what differences exist in the life-histories of the two insects.

.—Black; parapsides and lateral grooves the only well-developed thoracic grooves; foveæ irregular, not distinctly separated; legs rufous yellow; areolet moderate in size; length averaging 2.0 mm. : At least as wide as the thorax, the eyes large, bulging beyond the sides of the head; piceous black, toward the mouth and on the mouth-parts more piceo-rufous; very finely rugose, very finely and sparsely hairy. Antennae light yellow-brown, golden yellow basally, pubescent, 15-jointed, the last segment not shorter than the preceding, the third segment approaching twice the length of and more slender than any other. : Elongate; piceous black to black; posteriorly about smooth, mostly finely coriaceous antero-laterally; parapsidal grooves distinct, less so anteriorly, gradually and then widely divergent anteriorly, gradually convergent posteriorly, but still fairly well separated; median groove absent; anterior parallel lines hardly indicated; lateral lines not very well defined; scutellum narrow, longer than wide, slightly hairy, rugose, depressed and smoother anteriorly but with the two irregular and slightly rugose foveæ not distinctly separated by the rugose intermediate area; pronotum rugose, more rugoso-aciculate posteriorly; mesopleuræ in part smooth and shining, irregularly aciculate