1903.] 



11 



T think it may be well to begin my papers with some definitions 

 of technical terms that will from time to time have to be employed 

 in them. 



Taking, then, almost any saw-fly — gay, for instance, Tenthredo mcsoviela, L., 

 one of our best known species — and starting with the head as viewed from above, 

 we find just behind tlie posterior ocelli a quadrangular space bounded laterally by 

 distinct furrows— this is the "Scheitel" of Konow, we may call it the "vertical 

 area." The spaces bordering the compound eyes are the "orbits." Tlie space, in 

 which lie the ocelli, reaching from the vertical area to the insertions of the antennce 

 ia ihc " frons." Part of this space is surrounded by a system of five furrows, 

 more or less distinct in different genera, producing what is called the pentagonal 

 area • its apex lies a little below the front ocellus. Then, looking at the insect's 

 face, the prominent " cl^peus" appears just below the antennse, and below its some- 

 what " emarginate " apex is seen the subtriangular " labriim." The space between 

 the eye and the base of the mandible, rather shoi't in the present case, is the 

 "ffena" -^ " Wangenanhang " of Konow (better seen by looking at the insect 

 sideways). 



The back of the head, facing the thorax, is the " occiput." Between the 

 occiput and the compound eyes lie the " tempora," which in this species are "dis- 

 tinctly margined," i. e., separated from the occiput by aii evident raised edge. 



(I should perhaps have said before that the term " orbit " is often used rather 

 loosely, chiefly in descriptions of colour, to denote any region adjacent to the eyes. 

 Areas called "orbits" in this sense may often be a part of the genre or tempora, 

 and in measuring the latter for descriptive purposes one always measures right up 

 to the eye, i. e., not merely up to any coloured margin which may happen to 

 surround it). 



The details of the thorax, which furnish many very important 

 characters, can hardly be made clear except by diagrams. I give 

 therefore now an outline camera lucida sketch of the thorax in 

 Tenthredo mesomela, L., viewed from two aspects — (fig. I) dorsally, 

 i. e., from above, (fig. 2) laterally, i. e., from the side. 



Fig. 1. Fig. 2. 



