BY R. J. TILLYARD. 603 



away in crevices or under stones, where this type of specialisa- 

 tion would be of value for concealment. The working out of 

 the life-histories of this remarkable insect, and its ally Notio- 

 thauma should certainly be undertaken by those living where 

 these insects occur, and may be confidently expected to add much 

 to our knowledge of the Mecoptera. 



Table of the Principal Venational Characters for the 

 Families of the Order Mecoptera (Table i.). 



In presenting this Table, I have had to divide the Order into 

 a number of distinct families, some of which have not so far 

 been definitely recognised. The Choristidae will include the 

 genera Taeniochorista and Chorista, confined to Australia, and 

 distinguished from the Panorpidae (s. str.) by many good 

 characters, one of which is the presence of a five-branched media 

 in the forewing, and the presence of only four branches to Rs 

 in both wings. I have already defined the Permochoristidae 

 (6) . But I cannot find any good distinctions between the 

 Triassie Mesochorista and the Permian Permochorista, and am 

 convinced that these two genera must be placed in the same 

 family. Consequently the family name must be changed to 

 Mt so choristidae, since that genus was defined first (20). The 

 characters of the Ortlwphlebiidae have already been defined by 

 Handlirsch (2, p. 479), and those of the Stereochoristidae (28) 

 and Nannochoristidae* by myself. The Meropidae may be made 

 to include provisionally Notiothauma as well as Merope, though 

 the venation of the former has not yet been thoroughly worked 

 out on modern lines. The Bittacidae are a very distinct group, 

 witli very definite wing-characters; while the Boreidae, being 

 wingless, are omitted from the Table. 



In the Table, the archaic condition of any given character is 

 indicated by the letter A, while more specialised conditions are 

 indicated by B, C, . . .in ascending order. The Arche- 

 type of the Order is the type which possesses the condition A 

 for all characters. The percentage of archetypic characters pos- 

 sessed by the most archaic representative of each family is 

 shown in the bottom line of the Table, and affords an interesting 

 comparison of the relative archaism of the different families, as 

 tar as their wing-venation only is concerned. 



•These Proceedings, xlii., part 2, 1917, pp. 284-301. 



