47° CALIFORNIA ACADEMY OF SCIENCES. 



The flattening of the head, with the great development 

 of the clypeus, and the restriction of the mouth-parts to 

 the ventral aspect of the head, so characteristic of the 

 Mallophaga, is quite as characteristic of Atropos, the 

 wingless, degraded Psocid. Among the winged Psocid;e 

 the head hangs vertically, and although there is a similar 

 great development of clypeus, there is less flattening of 

 the head and less general resemblance. The peculiar 

 condition of the labrum in the Mallophaga, lying as it 

 does on the ventral aspect of the produced clypeus, finds 

 an identical repetition in Atropos; a point which Packard 

 seems to have overlooked when he says that the Mal- 

 lophaga differ from the Psocids in having the labrum 

 covered by the clypeus. In the winged Psocidce the 

 head is not horizontal as with the Mallophaga and Atropos, 

 and the labrum is attached to the ventral margin of the 

 clypeus. 



The mandibles of Atropos present a really striking 

 similarity with those of the Amblycerous Mallophaga. 

 The details of teeth, condyles, facets, and musculation are 

 extraordinarily alike. 



The maxillae of the Psocidas are greatly reduced, re- 

 taining, however, a well developed palpus. In the Mal- 

 lophaga the reduction of the maxilla? is carried still farther, 

 the palpi having become completely atrophied. 



The labium of the Psocidas (of Atropos in particular) 

 and of the Mallophaga is modified along essentially simi- 

 lar lines. One important distinction, however, is the 

 presence of well developed labial palpi in one suborder 

 of the Mallophaga. 



Not brought out in any previous discussion of the Mal- 

 lophagous mouth-parts, and, perhaps, more striking than 

 the points of resemblance so far noted, is the practical 

 identity of the oesophageal sclerite and accompanying 



