415 



triangular cardo (cd) ; a narrow sclerite which may be known as the 

 cardella (cl) ; and a long, oblong stipes, to the distal end of which 

 are attached two appendages representing palpus, lacinia, and galea. 

 The lateral, narrower one of these (mxp), the palpus, bears on its 

 surface a number of strong setae. There is sometimes a distinct swell- 

 ing at the base of it but there is no distinct suture between the proximal 

 and distal portions. The remaining process, regarded as the fused 

 galea and lacinia (glc), is much broader at the base and tapers con- 

 siderably at the apex, where it bears about five strong hooks. It is 

 provided with two rows of weaker setae extending proximad from 

 the hooks. The identification of this piece as fused galea and lacinia 

 is due to the supposed occurrence, in adults of certain species, of a 

 suture extending across it from the proximal to the distal end. So far 

 no case has come to my notice in which this suture is present, but a 

 study of Ephemerida (Morgan, '13) and Plecoptera (Fig. 31) on the 

 other hand, proves conclusively that the piece has been correctly inter- 

 preted. 



Labium. — The labium differs greatly from that of the ordinary 

 insect in being free from the head at the point of articulation of the 

 submentum, and in being folded so that mentum and submentum are 

 approximated when the piece is at rest. It is applied to the ventral 

 surface of the head, forming a sort of mask ; and an idea of its general 

 location and shape may be obtained from Figures 1-4, 6, and 7. 



Several forms of labia occur in the suborder which, although sim- 

 ilar in general construction, differ in certain particulars. The forms 

 of the lateral arms or labial palpi, the mentum, and the submentum 

 are different enough in different species to enable one to determine the 

 family, and sometimes the genus, at a glance (Figs. 8-13). The sub- 

 mentum is a hollow tube of cuticle (Figs, 2, 4; sm) articulating 

 at its proximal angles with the ventral wall of the head capsule. 

 It is filled with muscles for . the extension and retraction of 

 the labium as a whole, and varies in shape from cylindrical 

 to flat, and from comparatively short, hardly extending caudad 

 of the posterior margin of the head, to long and slender, reach- 

 ing caudad of the metacoxae. The mentum-ligula, or median 

 lobe (Figs. 8, 9; ml), is likewise filled with heavy muscles which 

 move the labial palpi. It varies in shape, in the degree of the con- 

 traction proximad, and, more important for purposes of classification, 

 in the number of mental setae (Figs. 10, 12, 13 ; ms). The median lobe 

 is sometimes notched or cleft at the apex but is more frequently with- 

 out indentation. The glossae and paraglossae are present at the distal 

 end of the labium, but the suture between them and the mentum is in 



