PROC. ENT. SOC. WASH., VOL. 20, NO. 2, FEB., 1918 29 



no traces of either ocellar pigment or lenses. The lateral margin 

 of the epicranium is thickened into a conspicuous, dark, heavy 

 endoskeletal ridge (LtR) articulating at the lateral angle of the 

 antennal ring and continuing back to where the dorsal and ventral 

 hind margins unite on the lateral edge; from here it divides 

 apparently into two arms, one curving around the dorsum and 

 forming the dorsal hind margin and finally fusing without ap- 

 preciable articulation with the adfrontal ridge, the other curving 

 similarly on the venter and fusing (also without articulation) 

 with the long ridge (Hr) of the hypostoma. This lateral ridge, 

 the peculiar development of the hypostoma. and the modification 

 of certain of the mouth parts are the most striking and significant 

 characters of this unique head. The triangular plates of the 

 hypostoma (Hp) which in most Lepidoptera are well back on 

 the ventral surface of the head, are in Opostega thrust forward 

 until they lie immediately under the epistoma and pleurostoma. 

 The endoskeletal ridge of the hypostoma (Hr) extends back- 

 ward from the triangular plates to the ventral hind margin 

 rather than forward from them as in normal generalized forms, 

 almost the entire mid-ventral surface of the capsule being occu- 

 pied by a thin transparent gula (GL). The tentorial bridge (TR) 

 of other lepidoptera is in Opostega a complete ring set well back 

 in the head. The articulation of the ventral arms of tentorium 

 (VaT) are at the extreme posterior limits of the hypostoma 2 

 and the epicranial fossa (Fs), for the mandible, which in all 

 other forms is a socket in hypostoma at the anterior end of the 

 hypostomal ridge is, in Opostega, a hole in hypostoma partially 

 or perhaps completely limited by the triangular plate. The 

 condyle of the mandible is thrust into this hole and the mandible 

 thus firmly locked into the head, a specialization, which as far 

 as I know, is not found in the Lepidoptera outside this family. 

 There is also a very unique structure on the mandibles. In 

 place of the two dorsal setae commonly found on most lepidop- 

 terous mandibles we have in Opostega a long, thick, tapering, 

 membraneous cone (Cn, fig. 7) projecting well forward of the 

 mandible. From its structure and position we may assume that 

 it is used as a brush to sweep into the mouth the fine, torn frag- 

 ments that are not carried in by the mandibular teeth, or that 

 it is used to sweep and clean the dorsal surface of the lower mouth 

 parts. The mandibles themselves are broad and considerably 

 flattened. They approach somewhat the flat mandibles of cer- 



- In normal forms the attachment of tentorium to hypostoma is to the 

 triangular plates (the inner invaginated area of hypostoma). hi (>/><<tega 

 the triangular plates are so reduced and so completely restricted to the 

 forward part of the head that the ventral arms of tentorium appear to, 

 originate directly from the endoskeletal ridge (Hr). 



