Sept., 1912.] Matheson : Haliplid.e of North America. 159 



spines. The shapes of the spines differ in the two genera (Figs. 3 

 and 5). The palpus is 4-segmented. In Haliplus the last segment is 

 subulate, shorter than the preceding one. Sensory pits are few and 

 scattered. In Peltodytes the last segment is conical, longer than the 

 preceding one and the whole palpus bears many sensory pits (Fig. 5). 



The labium is well developed. The submentum is large, trilobed, 

 the outer lobes prominent. The median lobe is entire in Peltodytes 

 (Fig. 9), emarginate in Haliplus (Fig. 7). In Peltodytes the mentum 

 is small and the suture separating it from the glossse and the para- 

 glossse is lacking. However the two prominent setae situated near the 

 median plane of the distal end of the labium and the lateral sutures 

 indicate the positions of the fused glossse. The paraglossse are fused 

 with the mentum at their bases. A few sensory pits are present along 

 the distal margin of the labium. In Haliplus the mentum is large 

 and separated from the distal part by a distinct suture. The glossse 

 and paraglossse are fused though the two prominent setae indicate 

 clearly the position of the glossas (Fig. 7). Many large, deeply 

 sunken set^e are found on the distal portion of the labium. One is 

 shown in detail in Fig. 8. These peculiar structures are probably 

 sensory. 



The labial palpi are 3-jointed. In Haliplus the last segment is 

 subulate and shorter than the second ; in Peltodytes it is conical and 

 longer than the second. The palpiger is large and prominent, espe- 

 cially so in Peltodytes (Fig. 9). 



The pronotum is narrowed in front, partially overlapping the 

 head. In Brychius the pronotum is quadrate, not narrowed in front. 

 The posterior margin is angulate, the projecting angle fitting closely 

 in between the bases of the elytra and concealing the scutellum. The 

 presternum is large, broad, and steeply declivous in front, fitting 

 closely over the posterior portion of the head. Posteriorly it almost 

 conceals the mesosternum and fits closely over the projecting median 

 portion of the metasternum. This solid union with the mesosternum 

 beneath and the metasternum behind adds greatly to the rigidity of the 

 skeleton. The episternum does not reach the coxa, being separated 

 from it by the forward projection of the epimeron (Fig. 11, cm). 

 The epimeron is narrow. Its inner edge projects between the epi- 

 sternum and coxa and reaches the prosternum in front. It thus forms 

 the lateral margin of the coxal cavity. The coxal cavities are open 

 behind (Fig. 11, c). 



