176 [August, 



pleurae, (4) the ventral as well as the dorsal surface of the abdomen, 

 and (5) the saw-sheath [if it be a ? ] in the ventral and lateral aspect 

 as well as in the dorsal, and in its natural position^ not pulled about 

 or crushed out of shape in the process of " setting." 



Although the Nematides undoubtedly form a good and distinct 

 group among the saw-flies, so that a collector of any experience would 

 seldom be in doubt whether or no a particular specimen belonged to 

 it, I am not aware that there is any one character peculiar to the 

 group and exhibited by all the members of it. Most of its genera, 

 but not all, have a common and easily recognised type of alar neura- 

 tion which combines the following characters : (1) an undivided radial 

 cell ; (2) four cubital cells, the first shortest, and the second re- 

 ceiving both the medial nerves ; (3) a petiolate humeral area ; (4) the 

 basal nerve strikes the subcosta before the origin of the cubitus and 

 after an intercostal nerve which is regularly present and distinct ; (5) 

 the hind -wings show "two discoidal closed cells," and a "complete 

 humeral area " (e. p., the humerus is not obliterated but distinctly 

 visible from its origin till it falls into the brachius). Quite four-fifths 

 of the Nematides may be recognised as such by possessing this neu ra- 

 tion. What is distinctive in it, however, is not any one of the above 

 characters separately, but their co-existence. 



Several characters on the contrary might be mentioned, the 

 absence of any one of which would at once show a specimen not to 

 be a Nematid. It cannot e. g. be one, if {a) the eyes reach up to the 

 mandibles (" gena? nullfe ") ; or if (&) the humeral area is not either 

 petiolate or " longly contracted ;" or iC {c) in the hind-wing there is no 

 discoidal cell, or one only, or if the humerus is obliterated. (Exception 

 must be made of course for " monstrosities," which may upset any 

 rule however general). Again (</) all Nematides have 9-jointed an- 

 tennse, and these are nearly always setiform. 



In the next paper I hope to give Tables of Specific Characters for 

 determining British Nematides, or rather such British Nematides as 

 are actually known to me. These, doubtless, are not all that exist in 

 this country, nor are they even all that have been recorded as British. 

 But I believe they include most species that my readers are likely to 

 meet with in most districts ; and I have said all along that these 

 papers are Notes only, and do not profess to be exhaustive like a 

 Monograph. 



