of certain species of Willow. — Part 2nd. 237 



way in which this can be so readily and conveniently done, as by as- 

 certaining the number of the ventral joints, viz: S 8, 9 6. 



II. In Mr. Norton's earlier papers on this family, probably through 

 some clerical or typographical error, he speaks of three recurrent ner- 

 vures. while in reality there are never more than tiro in the Hymen- 

 opterous wing. In his latest papers this is silently rectified. (Compare 

 on the one hand Proc. B. S. N. II., 1861, G. Dosytheus p. 151, G. 

 Emphytus p. 154, G. Nematus p. 157. and G. Selandria p. 219, with 

 on the other hand Proc. B. S. X. II., 1862, G. Tenthredo, p. 116.) 



III. The number of legs and prolegs in the Tenthredinidous larva 

 appears to be often inconstant in a given genus. For example, some 

 Hylotoma larvae are 20-footed, some 18-footed; (Westw. Introd. II. p. 

 97 ;) some Tenthredo larvae are 22-footed, some 20-footed; (Ibid;) and 

 Mr. Norton, probably on the authority of Hartig, asserts the same 

 thing of the larva of the allied genus or rather sub-genus Selandria. 

 (Proc. B. S. N. II, p. 219.) It has generally been stated that the 

 larva of Nt mains is always 2U-footed ; but unless I have been deceived 

 in my Nematus s.pisum, n. sp., the larva in this genus is occasionally 

 18-footed, the anal prolegs being obsolete. 



IV. Westwood, Dahlbom and Hartig, as quoted by Norton, divide 

 the larv;>3 of the genus Nematus into three groups, a, Solitary, feeding 

 on leaves, L, Social, feeding on leaves; c, Living in the galls of plants. 

 (Proc. B. S. X. If., 1861, p. 157.) We may now, from the facts first 

 ascertained by myself, sub-divide group c as follows : — c, Gall-makers, 

 living in galls made by themselves; d, Inquilines or guest-flies, living 

 in galls made by other species of Nematus <"r by Gecidomyia. As will 

 be hereinafter shown, there are also gall-making Euura and inquiliuous 

 Euura. In Cynipidx there are tolerably well-marked structural cha- 

 racters, which, as a general though not perhaps as a universal rule, 

 separate the Gall-makers from the Inquilines; (Proc. &c. II, pp. 477 

 — 8;) but I can detect none such either in the Tenthredinidous geue- 

 T& Nematus and Euura or in the Oecidomyidous sub-genera Cecidomyia, 

 Diplosis and Lasioph /<>. all five of which contain some species that are 

 gall-makers and some that are guest-flies. It does not follow, how- 

 ever, that a thing does not exist, because at present it has not been 

 discovered. Observe that no Tenthredinidous genus, with the single 

 exception of Pristophora (P. sycophanta, n. sp.) — a genus which is 

 little mure than a subgeneric form of Nematus — and no Ceeido- 

 myidous sub-genus is ever inquilinous, unless it also contains species 

 that are true gall-makers. Now, if species were primordially created 



