DISEASES OF THE ROSE. 207 



somewhat resembling a club. The greater part of its body is red, except the 

 head, the upper part of the thorax, the marginal point of the upper wings, and 

 the circles of the tarses, which are all black. It is from three and a-half to four 

 lines long, by one in thickness. The antennse are covered, united, but not articu- 

 lated. Those of the male are fine hair : their wings are transparent, thin as the 

 peel of an onion, and reticulated by close lines ; there are two wings near the 

 head, called the superior — and two farther removed, called the inferior. The head 

 is quadrilateral and long, the eyes long and whitish, and the abdomen seems to 

 confound itself with the thorax, whose shell, black, cordiform and swelling, ter- 

 minates with a yellow color. This abdomen has nine distinct rings, is some- 

 what compressed downward ; the posterior extremity is obtuse, slit longitudinally 

 for the protrusion of the saw in females, crosswise and open in males. 



This insect flies with difficulty, and is easily caught with the fingers upon the 

 full-siaed leaves of the rose-bush, where it lies all day, from May to August. Its 

 appearance is, at least, fifteen days later than that of the white-footed fly. But it 

 is less numerous toward the end of the season, when isolated individuals alone 

 are seen. 



The white-footed fly comes into the ancient genus Tenthredo of authors, and 

 of Saint-Fargeau particularly, and also the genus Selandria of the moderns. Its 

 abundance at the time the rose-trees are attacked, and the cessation of the malady 

 upon its disappearance, give reason to suppose, with a degree of probability, that 

 they are the cause of it. This genus is characterized by two radiated cellules and 

 four cubitals, unequal at the superior wings, antennae articulated and small at the 

 end. It is black all over, except the feet, which are pale white. It is one and 

 a fourth line long, and a-fourth in thickness. Its antennas have nine joints, and 

 are somewhat small at the end. The wings are transparent, very thin, with 

 dusky nervures, and completely folded on each other, when it becomes cold by a 

 change of temperature. Cold does not always injure them. On*the seventeenth 

 day of April, 1842, the temperature was at two degrees of Reaumur, and yet I 

 took a small worm out of the arm-pit of the leaves of one of my rose-trees. The 

 superior wings are nearer to the head, which is quadrilateral, with a large eye 

 on each side. The abdomen of the females is terminated by a point or sort of 

 saw, while that of the males is obtuse. They have a small white shell on the 

 shoulders, at the insertion of the antennae. The feet are whitish, excepting in 

 some individual the moiety of the thigh nearest the abdomen, which is black, and 

 appears to constitute a variety of this insect. In this species, as in the red-fly, 

 females are but one-tenth the size of the males, and the white-footed are twenty 

 times more numerous, and one-half less than the red species. It is born in April, 

 as I have before stated, and ceases to show itself about a month after. This fly, 

 which is perfectly smooth, does not appear to hatch after this period. At least, I 

 have not observed it later, while I have seen the red-fly most of the year. 



In the cool of the morning, and in particular localities, the white-footed-fly is 

 seen to form whirlings around rose-trees. Its smallncss and agility make it 

 difficult to catch, otherwise than with a net. 



I have sometimes found them dead, in the arm-pits of the leaves, probably 

 after they had laid their eggs. 



M. Geserin Menneville, to whom I sent this white-footed-fly, thinks it a new 

 species, distinct from the Selandria allApes (or Tenthredo morio), and the Selandria 

 pailescens of Gmclin. He wishes to call it Selandria Meratii ; but I prefer to give 

 the name of Excavator, as in my first notice, and to term it the Selandria Excava^ 



