1878.] 295 [Burgess. 



office, as characteristic of the Psocidas as the maxillary fork. Their 

 sac-like structure would suggest that they were salivary reservoirs 

 rather than glands, but I have not succeeded in finding any trace of 

 other glandular organs, or of ducts which might lead to them. 



Compared with Psocus, the mouth parts of the book-louse (Atro- 

 pos) may be distinguished by their greater development. The cly- 

 peus is even more vaulted; the upper lip has been described above; 

 the mandibles are stronger and much more denticulated; the maxil- 

 lary fork is more slender, and very elongate, its base reaching far 

 back into the head, and the tines are longer. The lobes of the la- 

 bium are also slenderer and longer, and the labial palpi are longer 

 and club-shaped. The lingual glands, from their yellow color, are 

 very conspicuous when the head is examined by transmitted light. 

 They are somewhat heart-shape instead of oval, and their ducts are 

 rather longer than in Psocus. (See figs. 11 and 12.) 



As the eyes of Atropos have never been described, I add a figure 

 (13) to show their composition of seven simple ocelli, arranged in 

 three rows. Six of these ocelli are round, and the seventh and 

 uppermost elliptical. 



I am indebted to the kindness of Mr. J. H. Emerton for the speci- 

 mens of Psocus examined. They were collected at Hamilton, Mass., 

 and are all pupal forms. 



EXPLANATION OF PLATE 8. 



Fig. 1. Head of Psocus in profile, d. The vaulted clypeus. I. Labrum. 

 m. Mandible, behind which, and under the basal joint of the maxillary palpus, is 

 seen the outer edge of the lobe of the maxilla, mx. c. The cardo, and m. p. the 

 palpus of the maxilla. /. The "fork," lying over the tongue, t., and fully ex- 

 tended; the base runs in behind the edge of the maxilla, mn. Mentum, and lb., 

 the labium with its one-jointed palpus, I. p. 



Fig. 2. Longitudinal section through the middle of same head. cl. Clypeus. 

 I. Labrum. mand. Mandible, the dotted line ends on the ribbed molar surface, 

 which tapers beneath into the sharp cutting edge. mx. Maxilla, t. Tongue. 

 /. Fork. lb. Labium, and I. p. its palpus, m. Mentum. I. g. Lingual gland, and 

 g. m., its suspensory muscle. a>.. (Esophagus opening below into the oral cavity, 

 at the base of which is the oesophagal bone, cs.b. f.m. Flexor muscle of the man- 

 dible, and I. m., the muscle of the labrum. c. m. Muscles of the clypeus. 

 gl. Supra-oesophageal ganglion. 



Fig. 3. View of mentum, labium, etc., from behind, m. Mentum; lb., labium, 

 I. p., one-jointed labial palpus, behind which one sees the tip of the fork,/. 

 c. Cardo ; p., stipes having the four-jointed maxillary palpus ; mx., lobe. Through 

 the mentum, can be seen the lingual glands, I. g., with their duct I. d. 



Fig. 4. View of the maxilhe, etc., from in front, as shown by a transverse sec- 

 tion of the head. rnx. Left maxilla, covering tip of right maxilla. /.. Eight fork, 

 its base imbedded in muscles; lig. its retracting ligament, ms. Socket of the 



