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Show 3(i0 PROF. WESTWOOD ON THE G E N U S P E R G A . [May 4, articulation. This structure appears to be nearly similar to that in some Neuroptera, as in Panorpa-the mentum sitting upon the conjoined membrane of the inner margins of the basal portions of the maxilla?. These parts being comparatively short, are incapable of being folded back as in the Cimbeces, and consequently he flat when at rest; the diminished size affects the palpi, which are all nearly alike in their dimensions, the maxillary pair having only four joints, and the labial pair three-characters which have hitherto remained unnoticed, by which they are distinguished from all the other genera of Tenthredinidee, which, as shown by Curtis (Brit, Entom.), have 6-jointed maxillary and 4-jointed labial palpi. The middle portion of the thorax (mesonotum) is, in many of the species, marked with an impressed longitudinal canal extending from the front margin halfway to the great scutellum. There are also two deep impressed lines extending from the middle of the inner margin of the dilated lobes of the collar, converging in the centre of the back and forming a sharp angle, which is often preceded by a hastate spot of a pale colour ; the sides of the mesonotum are also often longitudinally raised, the lateral margins being also acute and parallel. The scutellum is of large size, generally pale-coloured, and furnished at each of its posterior angles with a small projecting tubercle. This scutellum is followed by a joint which is clearly the representative of the metanotum (Comp. m y In trod. Mod. Class. Ins. ii. p. 115, figs. 2 & 3, s), and not the basal segment of the abdomen, from which it is generally separated by a distinct narrow membrane which is not seen to exist between the true segments of the abdomen. The abdomen of the males is generally short and truncate at the tips, and often setose on the upper surface, the setse or sericeous covering in one species (P. dorsalis, Leach) being so dense as to give a distinct colour to the dorsal patch. The wings are large or of moderate size, those of the males being smaller than those of the females; in the former, moreover, the stigma of the fore wing is large, and the anterior margin of the wing beyond the stigma is, in some species, obliquely truncate, giving quite a distorted appearance to the wing. This character was employed by Leach for one of his sections of the genus; but, being merely sexual, it is inadmissible for such a purpose. The transverse veinlets between the submarginal cells are often partially obliterated or bullated in the middle, the first being in a few species either quite lost or only partially indicated, upon which character (as seen in P. lewisii «Sc.) M . Guerin-Meneviile proposed to form a separate subgenus; but there is no clear line of demarcation in the species in this respect. The shape of the cells of the fore wings affords good specific characters. The marginal cell is always furnished at its extremity with a slender veinlet extending to the tip of the wing, the extremity of the cell itself being at a greater or less distance from the extremity of the stigma, the tip of the cell being sometimes quite acute and sometimes obtuse. The shape also of the third submarginal cell is also varied in consequence of the direc- |
