OF WASHINGTON, VOLUME XVII, 1915 175 



lobes, covering the floor of the buccal cavity wholly or in part 

 only, as the case may be. These lobes are generally clothed with 

 flexible lashes, with hairs or with rows of strong spines. They 

 attain various proportions in all directions; so far, I have found 

 that relatively to the size of the hypopharynx they attain their 

 greatest dimensions in some of the microlepidoptera. In many 

 instances the lobes are also furnished with chitinous blades, these 

 again, are subject to the most extreme modifications both as to 

 their general shape and to their location on the lobes. 



Although really distinct from the hypopharynx the chitinous 

 projections of the mentum 1 marking the exterior of attachmenl 

 of the maxillulae, should be mentioned in connection with these 

 organs, as they are, in some cases at least, subject to modifi- 

 cations of real interest. In Mnemonica auricyanea Wlsghm., 

 arms from the mentum enter the mouth cavity and are fused 

 at the base of the hypopharynx, forming a complete ring, with 

 a conspicuous plate at the point of fusion. The lobes of the maxil- 

 lulae originate at the forward edge of this plate. They appear 

 as membranous flaps, clothed on their inner edge with a row of 

 long cilia-like hairs. The appendicular nature of these lobes 

 can readily be recognized, as they can be laid to one side and of- 

 ten will take this position under the mere pressure of the cover- 

 glass of the microscopic slide. Slightly forward of the above 

 mentioned plate, we find on each side of the hypopharynx a row of 

 four or five minute teeth. These are a part of the maxillul;r. 

 but not the whole organ, as was inferred by Busck and Boving 

 in their paper on this species. (For figure, cfr. Busck and Boving 

 "On M. auricyanea" loc. cit. pi. XI, fig. 8). 



The mouth-cavity of Ectcedetnia In- in rich i Busck, presents a 

 totally different aspect from that of Mnemonica. Here, the arms 

 of the mentum suggest the shape of a boot. They are very slender 

 and reach only a short distance over the lateral edge of the hypo- 

 pharynx. From the extremities of these arms arise two fleshy 

 lateral lobes, somewhat corrugated in appearance and covered 

 with filaments and spines. They are partly hidden by the 

 blades. These consist of a set of enormously developed plates, 

 they overlap and cover the entire floor of the basal part of the 

 mouth-opening (cfr. pi 18, fig. 5). In a species of Gracilariu col- 

 lected on Alnus by Prof. Charles R. Ely, we find what might be 

 called a typical form of the modifications studied in this paper. 



1 The term "Mentum" is applied sensu Dampf: "Zur Kenntniss ^r- 

 hausetragender lepidopteren larven (loc. cit). It applies to the part desig- 

 nated as stipes labii in our paper "On Acroccrcops strigifinitella" (Proc. 

 Ent. Soc. Wash., loc. cit.); cfr. also Busck and Boving "On Mnemonica 

 auricyanea" (Proc. Ent. Soc. Wash., loc. cit.). 



