i8g2.] 



THE BRITISH NATURALIST. 



93 



does this difference present itself in the nocturnal predaceous ground- 

 beetles (Geodephaga) and in the carnivorous water beetles. Thus, 

 of the former may be quoted as examples: the duller females of both 

 British Licini ; those of most Calafhi ; of PtcrosticJiiis vitreus and P. 

 oblongopunctatus, and especially of P. striola where the female is much 

 more finely striate on tliC elytra ; Oodes Jielopioides ; most true Amavce 

 (in which the females appear more deeply striate) ; many Havpali, 

 such as H. tenebrosus, tardus, serripes, and most noticeably in the 

 females of H. ruhripes and discoideus which are dull and obscure while 

 the males are often brilliant blue, green, or metallic. In the Hydra- 

 dephaga (carnivorous water-beetles) it is quite common for the female 

 to be dull while the male is shining, as is seen in Hyphidnis ovatus, 

 many Hydropori, Agabus bipustulahis, the Gyrini, &c. ; while it is in 

 this group alone of the British Coleoptera that we meet with any 

 indication of sexual dimorphism, but which here, in a comparatively 

 small group of insects, presents itself in two forms. In the first and 

 most frequent of these, seen in Bidessus uni-stviatus, Ccelainbus 

 novemliniatus and picipes, Hydropovus erythrocephaliis and memnonius, 

 Agabus uliginosus, &c., the male, following the rule, is shiny, while the 

 female occurs in two forms, the one polished like (and scarcely 

 distinguishable from) the male, the other dull and opaque. Another 

 and more remarkable difference in the sculpture of the sexes is present 

 in the genera Dysticus and Acilius. In the first of these, where the 

 elytra or wing-covers of the male are smooth and very highly 

 polished, those of the females are deeply grooved longitudinally. It 

 is in this genus that we meet with the second form of sexual 

 dimorphism, for in all the British species except punchilatiis and 

 diinidiatus the female also occurs with the elytra not silicate, differing 

 only from those of the male in having some fine punctuation towards 

 the apex."^' In Acilius the elytra of the male are somewhat polished, 

 while those of the female are not only sulcate, but the grooves, which 

 are wider than those of Dysticus, four in number, are clothed with long 

 yellow hairs. In the genera Onthophagus and Ap>hodius, indeed in the 

 Scarabseidae generally, the head of the female is often more coarsely 

 punctured than that of the male; and in the Ap)hodii it is usual for 

 the male thorax to be punctured only towards the sides, leaving the 

 disc smooth, while that of the female has the punctures not only 

 coarser but sprinkled more generally over the surface. The males of 

 many Cryptoce^yhali are often more strongly punctured than the females. 



The only exceptions that I know to the rule that the female is the 

 duller sex occur in Lucajiiis and Dorciis. In Lucaiuis cervns the head 



* It is worth while to notice here that according to Canoa Fowler, ]")r. P.nver's 

 collection contains a female specimen of Dyslicns circunicinctus intermediate between 

 the two forms — shewing traces only of longitudinal sulci. 



