CHRYSOMELIDAE. 



191 



background is seen to be finely shagreened. Scutellum triangular, with 

 rounded apex, slightly convex, finely shagreened. Elytra regularly punctate- 

 striate, much broader at base than prothorax ; at base on inner side of 

 humerus is a convex area ; on each elytron are thirteen rows of punctures, 

 including a scutellar and an extreme marginal row ; counting from suture, 

 ninth and tenth rows arise from behind, and twelfth row arises from below 

 humerus, all being very short ; rows meeting in pairs on narrowed apical area. 

 Under side : legs of usual length in this genus ; femora thickened in middle 

 and without any spine ; middle and hind tibiae emarginate on outer side at 

 apex ; claws strong, bifid. 

 Length, 3 mm. 



Savaii : Safune, rain forest, 2,000-4,000 ft., 3.V.1924 (Bryan). 

 Type in the Bishop Museum. 

 Described from one example. 



The study of the Eumolpinae of the present collection lends support to an 

 idea which suggested itself to me when I was studying other island faunas, such 

 as that of the Seychelles. In that case also I was confronted with the same 

 difficulty of judging the limits of a species which showed structural variations. 

 The idea may be formulated thus : in island faunas species tend to become more 

 plastic than in continental faunas. I put forward this principle tentatively, 

 and its validity or otherwise will be proved as more experience is accumulated. 

 Mr. K. G. Blair tells me that he observed the same phenomenon in a Lycid 

 beetle, Samoaneros acuticollis Fairmaire (Part 4, p. 101 above). Dr. G. A. K. 

 Marshall also tells me that amongst the Samoan Curculionidae the same 

 feature is noticeable in some species. It would be premature to speculate here 

 as to the causes of such variation in island faunas. 



Chrysomelinae. 



9. Plagiodera samoana, sp. nov. (Text-fig. 8). 



Body ovate, strongly convex, highest point of convexity being middle of 

 elytra ; seen in profile, from this point upper surface slopes down more abruptly 

 in front than behind. General colour shining dark brown ; in some cases under 

 side is tinged with blackish, in others it is pitch-black ; head and pronotum always 

 brown ; elytra pitch-black. Among nine examples before me, in one the pitchy 

 colour is lighter and in two it has become brown, except the apical area of the 

 iv. 3 2 



