On Aquatic Carnivorous Coleoptera or Dytisciche. 533 



has the meshes of the reticulatioa on the el3'tra comparatively broader and shorter, 

 and the prosternal process less compressed at the sides. 



Europe, throughout, from Iceland and 69° North according to Sahlberg, to Spain and Portugal ; Corsica ; 

 Sardinia, Sicily, Algeria, Syria, Persia. 805. , . 



The variation found in this species is very complex and interesting. The ordinary 

 form may be considered to be that in which the female has the surface duller than 

 the male and the longitudinal scratches finer, denser and more oblique, the general 

 form in both sexes being rather regularly oval, the female however being generally 

 just a little narrower and more oblong than the male : on examination under the 

 compound microscope with a half-inch object glass, it appears that the dullness of 

 the surface in the female is caused by minute scale-like reticulations, which are 

 not so deep in the male as in the other sex : this form is that universally found in 

 temperate Europe, and I have it in my collection from as far east as Persia : the 

 size about 9 — 11 m.m. long, 5 — 52 m.m. broad: this maybe called the ordinary 

 or typical form. In some of the warmer parts of Europe, there are found large 

 specimens in which ihe sculpture in the female is quite similar to that of the male, 

 which, as in the ordinary form just mentioned, consists of very elongate, narrow 

 meshes on the basal portion of the elytra : this may be called the South European 

 variety. In the highland districts of Britain, and in the Alps and Iceland, the 

 specimens become smaller, and of a narrower, more oblong and depressed form 

 with the base of the thorax narrower than that of the elytra, and tlie surface in 

 the female excessively dull, so that the disparity in the appearance of the two sexes 

 is very great : but this form (for females of which Aube proposed the name " Agabus 

 solieri") is connected with the common temperate European form by every shade of 

 intermediate variation: this maj' be called the dimorphic Alpine form. In some 

 localities in the Alps and Pyrenees there are found (I believe always at a great 

 elevation) specimens of elongate, narrow and depressed form, with very shining 

 surface, the sculpture in the female being similar to that of the male, and the meshes 

 of the reticulation of the elytra are generally rather broader and shorter than in 

 the ordinary temperate European form. This form has been found by Kiesenwetter 

 in the Alps of Carniola; and has also occurred at Lago Pinter, and in the Hautes 

 Pyrenees; it may be called the monomorphic .A.lpine form. We have thus the 

 peculiar anomaly that in some Alpine districts the sexual divergence in sculpture 

 of the female from the male is much increased, while in other Alpine districts there 

 is on the contrary convergence of the sculpture of the female to the male, or in fact 

 absolute similarity. I have no evidence that these two Alpine forms of the female 

 are ever found together, indeed all the evidence I have indicates the contrary ; thus 

 though I have found great numbers of the dimorphic Alpine form in the mountains 

 about Braemar, I have never found a single female with sculpture at all like that 



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