A GUIDE TO THE STUDY OF BRITISH WATERBUGS. 177 



no reason, apparently, why it should not occur with us, as it is 

 ver}' common in France as near as Paris, and also in Belgium. 

 I have taken it plentifully in South Brittany. As it is a possible 

 British inhabitant, it is now described and figured (fig. 35). It is 

 smaller than Ilyocoris cimicoides, greenish testaceous, marked 

 with brown. The pronotum is marked with a distinct, inverted, 

 brown W. The tibia? are longer, less robust, and not so spinose 

 as in the common species. The most marked difference, however, 

 lies in the anterior femora, which are very greatly thickened, 

 and suddenly ampliated in a right angle at the base beneath, 

 then narrowed (fig. 36) ; the pad of hair on the femora is also 

 much smaller, and occurs only near the base. The species, 

 unlike I. cimicoides, is dimorphic. While I. cimicoides varies 

 from 12-16 millimetres in length, N. maculata averages about 

 10. The brachypterous form was described as a distinct species 

 by Dufour under the name of Naucoris aptera. 



This bug is the type of the genus, and was described originally 

 by Geoffroy (1762, ' Histoire abregee des Insectes de Paris,' 

 p. 173, pi. ix. f. 5) as Naucoris cimicoides, under the impression 

 that it was Linne's species. There is also a coloured figure in 

 Herrich-Schaffer's ' Wanzenartigen Insecten,' ix. pi. cexciii. 

 f. 899, and detail F. E. D. (1849). It is said by Leon Dufour* 

 to lay its eggs at the end of April in a similar situation to those 

 of Ilyocoris. They are obtuse oval, not truncate. Dufour, in 

 the same work, gives much information on the digestive ap- 

 paratus, sexual glands, &c, of both these genera. 



Explanation of Plate II. f 



FIG. 



15. Gerris canalium, $ , apical abdominal sternites. 

 1«. „ ,, ?, „ 



17. G. naias, <$■>,, » ,, 



is. ,. 2, „ 



19. G. rufoscutellata, $ , ,, „ ,, 



20. „ ?, „ 



21. G. lateralis, $ , „ „ ,, 



22. G. thoracica, g, ,, „ ,, 



23. „ 2, „ 



21. G. costai, J , ,, ,, ,, 



25. G. gibbifera, J , ,, ,, ,, 



2(3. G. lacustris, J , ,, ,, ,, 



27. G. odontofjaster, $ , apical abdominal segments, viewed from the side. 



28. ,, 5 , apical abdominal sternites. 



29. Ilyocoris cimicoides, showing articulation of anterior legs. 



30. Notonecta glauca, ,, ,, ,, „ „ 



'■■'■ " Kecherches Anatomiques sur les Hemipteres," 1833, Mem. Savans- 

 etrangers Acad. Roy. Sci. France, iv. pp. 349. 413, &c, pi. xvi. figs. 180-2. 



| This plate includes " PI. iii.," mentioned in vol. xxxii. pp. 202-3 (1899). 

 (Figs. 33, 37-44 are omitted.) 



