3G0 PROF. WESTWOOD ON THE GENUS PERGA. [May 4, 



articulation. This structure appears to be nearly similar to that ob- 

 served in some Neuroptera, as in Panorpa — the mentum sitting upon 

 the conjoined membrane of the inner margins of the basal portions of 

 the maxillae. These parts being comparatively short, are incapable 

 of being folded back as in the Cimbeces, and consequently lie 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 jiair three — characters which have hitherto 

 remained unnoticed, by which they are distinguished from all the 

 other genera of Tenthredinidse, 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, con- 

 verging in tlie centre of the back and forming a sharp angle, which 

 is often preceded by a hastate spot of a ])ale 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. my Introd. 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 setae 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 &(:.) M. Guerin-Meneville 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 dis- 

 tance 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- 



