***. 



appears to spring. This organ we have called The Gnathos 

 (Ourapteryx, etc., pi. Hi.) (Wytsman, I.e. p. 6). It has 

 been mistaken for the Scaphium of the Papilios, with 

 which, however, it has no connection. It was figured in 

 the " Noctuidae " in the genus Brephos, but not named. 



This organ has appeared to me to be of such import- 

 ance as to form two primary divisions of the Geometridce, 

 according as it is present or absent, and for these divisions 

 I propose the names Gnathoi and Agnathoi. The species 

 falling within the Gnathoi, but having the gnathos 

 rudimentary or atrophid, are so few that they may be left 

 out of consideration. 



THE ANUS. 



At the base of the uncus on the ventral surface of the 

 tegumen is an opening through which passes the anal tube. 

 In the Agnathoi this tube is very long and is decorated 

 with spines (Perizoma didymata, pi. xxvi.}. Attached to 

 the under side of the tube is a thickened chitinised process, 

 generally taking the form of a plate, but sometimes that 

 of a hook, which I have previously named The 

 Subscaphium (" Noctuidse," p. 13). 



THE TEANSTILLA. Pierce. 

 From the bases of the valvee arises a cross-bar which 

 I term The Transtilla (Ennomos autumnaria , pi. iv.). The 

 cross-bar may be incomplete, the opposing arms not 

 uniting, and whilst it is often simple, it is capable of great 

 development, occasionally producing free arms, and 

 becoming in the Tortricida a highly complex part. 



THE NINTH SEGMENT. 



This segment is very probably represented by the 

 tegumen. It is generally composed of thin chitine, but it 

 sometimes resembles a normal segment. In the 

 Eupitheciince it is introverted and holds the genitalia 

 within the eighth segment, as in a bag. In this group also 



