Odonata from Neio Caledonia. 37 



wliich is evidently distinct from /. spinrpes, Seh^s (the geno- 

 type), and I. robustior, Ris. This I have pleasure in naming 

 after my friend Dr. R. J. Tillyard, whose visit to London 

 in the summer of 1920 gave me an opportunity of dis- 

 cussing with him several mutters of interest arising upon 

 Mr. Montague's collection. 



Although six species are now referred to Isosticta in all, 

 I have not seen any of those which occur o'utside New 

 Caledonia. . It is not possible from the literature alone to 

 make a complete comparison between them in respect of the 

 labium, the hitid margin of the prothorax, and the til)ial 

 armature, but, as will be gathered from the following ta1)le, 

 they do not present any great uniformity in certain vena- 

 tional characters of importance. The anal appendages of 

 the male, so far as they are known, are likewise wanting in 

 that general likeness of form which usually characterises 

 the members of a natural genus. Tillyard's description of 

 /. banksi was accompanied by some remarks on /. simplex 

 and /. spinipes (Proc. Linn. Soc. N. S. Wales, xxxvii. 

 pp. 432-3, 1913). After assuming that the genotype, " so 

 closely allied to 7. simplex in other respects, possessed also 

 appendages of a similar remarkable form,'' he went on to 

 say that " we may fairly consider the form of the male 

 appendages to be a generic character, which may be stated 

 as follows : * Both superior and inferior appendages of male 

 somewhat forcipate, the inferior pair prolonged beyond the 

 superior.' " As we have since learned, the inferior appen- 

 dages of /. spinipes are neither forcipate ' nor prolonged 

 beyond the superior, and consequently the proposed addition 

 to the generic definition cannot be accepted. Indeed, the 

 anal appendages of the two Australian species, /. simplex 

 and /. banksi, differ in a marked degree from those of the 

 genotype and its congeners from New Caledonia. 



As at present constituted, the genus Isosticta includes 

 within its limits four groups of not entirely accordant 

 species : — 



(1) Wings with M3 separating well in advance of 

 the subnodus, and Cui ending 4-8 (usually 5-6) 

 cells beyond the quadrangle ; lower anal ap- 

 pendages of the male as long as the upper .... rohustior, Ris. 



(l>) Wings with M.^ separating at or just before the 

 subnodus, and Cu, ending 1-2 cells beyond 

 the quadrangle ; lower anal appendages of the 

 male conspicuously longer than tlie upper. 



Upper appendages of S depressed sitnple.v, Martin. 



Upper appendages of (S straight b(mksi, Tillyard. 



(3) Wings with M;) separating at or just beyond the 



