THE CANADIAN ENTOMOLOGIST. 337 



genital plate in Diplonychus, as in Belostoma, is entire, while in Amorgius 

 it is deeply fissured medianly. In shape it is much the same throughout the 

 family, although much shorter in Belostonia than in the other two genera. 

 The tibiffi of the third pair of legs in Amorgius is flattened, more or less 

 broad, heavily fringed with long hairs, and terminates in two long claws. 

 Belostoma and Diplonychus, on the other hand, have prismatic posterior 

 tibiae, and the hairs are shorter. The form of the intermediate tibire is 

 the same in each genus as the posteriors. It is in the anterior pedes that 

 the most interesting features occur. The femora are incrassate in all 

 three, but while in Belostoma they are only moderately so, in Diplonychus 

 and AjHorgius they are greatly so. All three genera have them deeply 

 sulcate for the reception of the tibite, which are of similar shape in all. 

 The tarsal joints are moderately long and equal in Belostoma. In 

 .Ajnorgius 2LX\d Diploiiyc/uis \\\(ty dixe small ard unequal. The profound 

 yet most significant character is contained in the anterior tarsal claws. 

 These are single, long in Amorgh(S, and small in Belostoma. In Diplony- 

 chus they are double and long, though the outer is but half the length of 

 the other in the two species known to me, while in one described by Mayr 

 they are of equal length. The importance of this structural feature can 

 be appreciated only from the study of the nymphs taken in conjunction 

 witli the changes that occur in the claws during development. As various 

 authors" have from time to time pointed out, Belostomatid nymphs of the 

 several genera are all two-clawed in the anterior tarsi throughout all, or in 

 some of the earlier, instars. In general, the nymphs ol Amorgius possess 

 two elongate ecjual claws up to the last moult, one of which they lose at 

 that ecdysis, and the adult has only one more or less long tarsal claw. In 

 the several nymphs oi Belostoma, as I have elsewhere noted,'* some lose 

 the one claw early, others by slow stages,^^ at some one of which the length 

 of one claw bears the same relation to the other as the adult in 

 Diplonychus known to me. In this last-named genus, however, the 

 nymph in the last instar has the two long claws of equal length,'" as in 

 Amorgius. At the last moult in two species one of these claws is reduced 

 to half the length of the other, while in the third, known to me only by 

 description, the two equally long claws are preserved. 



13. 1863, Dufour, op. c; 1871, Mayr, op. c. ; 1901, Howard, Ins. Rk., p. 279 ; 

 1906, Bueno, Can. Ent., XXXV'III, p. 197 ; and others. 



14. Op. c. 



15. Cf. B. fluminea, op. c. 



16. Duf., Ann. Soc. Ent. Fr. (A. )III, p. 386, description of nymph in last 

 instar of Hydrocyrius algeriensis. 



