1914.] ]35 



natator, and still more to that of oblitus. Indeed I do not perceive any 

 distinction in the axleagus of several species of the genus that I can 

 rely on as satisfactory evidence of specific distinction. 



6. Gr. bicolor Payk. 



This species is not difficult to distinguish on account of its very 

 elongate form, and the strongly rounded apices of the elytra. Schiodte's 

 G. celox is referred to in the catalogues and books as a synonym of 

 bicolor, but the form of the apices of the elytra in his beautiful figure 

 shows that it refers to G. elongatus var. angustatus, and this was 

 Schiodte's own opinion. The sedeagus (figs. 9) is very different from 

 that of G. elongatus. The figure given of the median lobe of G. bicolor 

 by Mr. Edwards shows an unnatural amount of constriction in the 

 middle. 



7. Gr. COLYMBUS El'. 



G. caspius Sharp, Ent. Mo. Mag., v, 1868, p. 57. 



This species is intermediate in shape between natator and elongatus, 

 and this is the best character for its recognition. There is an extremely 

 fine diffuse punctuation on the elytra, but this is so difficult to study 

 that it is better to rely on the shape for distinctive purposes. The 

 oedeagus (figs. 7) is very distinct, on account of the very broad, blunt 

 median lobe, which, however, in immature specimens may shrivel so as 

 to become constricted at the base (figs. 14). 



Gyrinus caspius of Aube is said by Regimbart to be a mixture of 

 distinctus and elongatus. 



8. Gr. striolatus Fowler. 

 G. colymbus Sharp, Ent. Mo. Mag., v, 1868, p. 58. 



G. distinctus var. strigulosus Reg., Ann. Soc. ent France 

 1891, p. 677 (teste Fauvel, Rev. Ent. Franc, xiv, p. 92). 



A broad, robust species, almost equalling natator in these respects, 

 but distinguished from it and all others by the dense distinct sculp- 

 ture of the surface of the elytra. This sculpture consists of short, 

 fine, oblique scratches, and can be perceived with a comparatively low 

 magnification. It is similar in the two sexes, and exists on the prono- 

 tum in a somewhat modified form. Female G. marinus makes some 

 approximation by its sculpture. The sedeagus (figs. 8) is like that of 

 marinus and bicolor, but the terminal sharp part is very remarkable. 



9. Gr. opacus Sahib., nee auctt. 

 G. opacus var., Sharp, Ent. Mo. Mag., v, 1868, p. 59. 



