NO. 10 MORPHOLOGY OF GNATHOTRICHUS SCIIEDL 29 



margin of the lacinia numerous bristles (g) are scattered over the 

 entire lobe ; the surface is slightly reticulate. Basally, the united lacinia 

 and galea end in a lobe, the subgaleal area (d), which is distinctly 

 defined on the inner side by an impressed line. The galea bears a 

 short row of slender setae (k) on its free dorsal margin ; the surface 

 is armed with rather sparse, long hairs (e). 



Adopting the terms of other authors, it may be said the lacinia is 

 pilose on its dorsal margin and spinose on its posterior and that the 

 galea is spinose. 



Palpi. — The palpi (P) are three-jointed. The first joint is the 

 longest, the second and the third are subequal in length. Anteriorly 

 joints one and two bear setae, joint three punctures only. There occur 

 slight differences in the size and the' shape of the joints in the species, 

 but they are not distinct enough to be of importance. 



Labium. — The labium (fig. 13), consisting of the mentum, the 

 ligula, and the palpi mainly, presents the most important generic and 

 specific characters of the mouthparts. 



The shape of the mentum (fig. 13, M) is similar in all three species. 

 It is flask shaped, the palpi f era always being wider than the neck 

 (fig. 13, b) and the base of the mentum and the latter always nar- 

 rower than the ligula (fig. 13, L). The basal portion of the mentum 

 is feebly widened in Gn. retusiis Lee. (fig. 13, A) and strongly widened 

 in Gn. mater iarius and sulcatus (fig. 13, C). In Gn. sulcatus and 

 materiarius, the mentum and the ligula are separated by deep sutures 

 throughout, even at the extreme base of the ligula ; in retusus they are 

 similarly distinct except at the extreme base before which they com- 

 pletely disappear. The sculpture of the mentum on the ventral side 

 (fig. 13, C), except for a few distinct punctures, is smooth in Gn. sulca- 

 tus. Gn. materiarius is very similar but it shows slight evidences of 

 transverse wrinkles also. In Gn. retusus the punctures are obsolete ; the 

 wrinkles are strongly developed and become on the neck of the mentum 

 and the basal half of the palpifer more or less toothlike (fig. 13, A) . All 

 the setae are simple bristles (c), and there are eight to ten of these 

 bristles on each half of the ventro-lateral side of the apical third of 

 the palpifer. In Gn. retusus and materiarius there are ten of these 

 bristles ; in sulcatus eight is the usual number. 



Ligula. — In this genus, the ligula (L) is much larger and more 

 prominent than is usual ; it is wider than the mentum in its basal 

 half and is distinctly limited by sutures at the extreme base of the 

 labium except in retusus. The ligula (fig. 13, L) extends in all three 

 species a little farther anteriorly than the first joint of the palpus. Its 



