18!i8.] Ill 



view as to the thorax of TrocJiopus, which I find confirmed by an ex- 

 amination of the immature stages. In my figure of the young larva 

 of Trocliopus (fig. 11) it can hardly be doubted that the small paired 

 tergites behind the head represent the pronotum, and the much larger 

 pair, some distance further back, the mesouotum. In older larvae I 

 find that this latter grows forward in the neighbourhood of the longi- 

 tudinal central suture, until in the adult it overlaps the pronotum 

 with the central projection shown in fig. 1. Hence it seems that in 

 Trochopus we have the persistence in the adult of an early stage of 

 development, before the backward growth of the pronotum over the 

 mesothorax (so prominent a feature in the winged species of the group 

 and represented to some extent in most apterous forms) has begun. 

 This primitive thoracic structure is another character by whicb Tro- 

 cliopus may be separated from IthagoveJia. 



In my previous remarks on the afianities of Trochopus I took it 

 for granted (now it seems too hastily) that the insect was referable to 

 HalohatincB. Tet it appears to show as much resemblance to Halolates 

 and its allies as to Velia, and the study of such a type makes it 

 doubtful if the various sub-families of the Hydrometridce can be 

 de^nitely marked off from each other. Prof. Uhler, in the paper in 

 which WiagoveJia plumhea is described, mentions that a West Indian 

 species of MicroveJia (M. longipes) " helps to bridge over the gap 

 between this group and the Sydrohatincs.^^ 



Prof. Uhler writes that males and females of his B. plumhea were 

 secured in cop., and that the male is very much smaller than the female. 

 This observation shows that the specimen which I supposed to be a 

 male is really a female with ovipositor extruded, and that my figures 

 8, 9 and 10 must be referred not to the male but the female genital 

 apparatus. 



As no detailed figures of Ithagovelia seem ever to have been pub- 

 lished, I hope that the editors and readers of the Entomologist's 

 Monthly Magazine will forgive me for having made use of its pages 

 to publish a specific, if not also a generic, synonym. 



Science and Art Museum, Dublin : 

 April, 1898. 



[The name Trochopus can, perhaps, be retained for the salt water 

 insect described by Prof. Uhler and Mr. Carpenter. An allied species 

 — found by myself on salt water, in small creeks, on the Isla del Rey, 

 or San Miguel, the largest of the Pearl Islands, in the Bay of Panama — 

 which I intend to describe elsewhere, possesses all the structural pecu- 

 liarities of H. phimheus. In the male of the Panama insect the 



