42 CALIFORNIA ACADEMY OF SCIENCES. 



margin, or on the non-emarginated margin. They are 

 two in number, although each is sometimes slightly or al- 

 most completely divided by an angular emargination. 

 They are flatly convex to hemispherical, and clear to 

 strongly colored. 



The mouth parts (figs. 7, 8, 9, plate ii), situated on the 

 under side of the head, and variously from the middle of 

 this aspect to the frontal margin, are fitted for biting and 

 consist of rather large, strongly chitinized, usually two- 

 toothed, usually sharply pointed mandibles, inconspicuous 

 and as yet imperfectly known maxilla? without * palpi, and 

 a labium of various character and size ; either large and 

 with 4-segmented palpi (family Liotheidae) or small and 

 without palpi (family Philopteridas). Despite the good 

 work of Grosse the knowledge of the mouth parts of the 

 Mallophaga is still manifestly incomplete. 



Thorax. The thorax, which is composed usually of 

 but two segments (three in but three genera), the meso- 

 and metathorax being indistinguishably coalesced, is flat, 

 larger than broad, and variously shorter than the head to 

 much longer than the head (in one species as long as the 

 abdomen). The lateral borders of both sclerites are 

 strongly chitinized. The metathorax sometimes closely 

 resembles an abdominal segment and is often closely joined 

 to the first abdominal segment. The prothorax usually 

 bears one to a few stiff hairs on its lateral margins; the 

 metathorax often bears in addition to the hairs almost al- 

 ways present in the lateral angles, a series of long, strong 

 hairs ranged along the posterior margin. These hairs 

 may arise from small uncolored (unchitinized) spaces and 



"The earlier writers, Nitzsch et al., ascribe the visible palpi to the max- 

 illae; Grosse is positive of their labial connection. A study of the anatomy 

 of the Mallophaga, now being made in my laboratory, will, it is hoped, 

 afford some further data on the month parts subject. 



