On Aquatic Carnivorous Coleoptera or Dytiscidce. 117 



Group 4. 



1140. Dytiscus tripunctatus, 01., Tragus tripunctatus, 31. C. — Ovalis, supra 

 olivaceo-niger, capite anterius prothoraceque lateribus testaceis, elytris margine 

 externo (cum epipleuris) argute et sat late testaceo ; subtus piceus, metathoracis 

 episternis abdominisque lateribus testaceo-maculatis, pedibus quatuor anterioribus 

 testaceis, femoribus anterioribus fusco-maculatis, tibiis intermediis fusco-testaceis, 

 tarsis intermediis pedibusque posterioribus piceis ; antennis testaceis. Long. 

 22—31 m.m., lat. lU— 16 m.m. 



The anterior tarsi of the male are rather small ; their pubescent area is of mode- 

 rate size ; the intermediate tarsi have the two basal joints bearing well develojied 

 jiatches of moderately short sexual pubescence, and their claws are simple, very 

 little unequal, and in fact scarcely difierent from those of the female. The female 

 is either entirely without sexual sculpture, or may have on the basal portion of 

 the wing-cases, very short irregular isolated scratches ; the thorax never shows the 

 least trace of sexual sculpture. 



The species is very variable in size, form, and the sexual sculpture of the females, 

 and shows even considerable variation in the sexual pubescence of the intermediate 

 tarsi of the male, as well as in the width of the yellow marginal cincture which 

 varies on head thorax and elytra. I have made a careful review of its numerous 

 variations, and give below the results. It may be said roughly that there are four 

 forms, an Eastern Asiatic one found in China, Japan, Formosa, Mantchuria, 

 Philippine Islands, Malay peninsula, Hindostan, and Ceylon, — as well as in Austra- 

 lia ; while the New Caledonia individuals approach the second form which is found 

 in the islands of the Malay archipelago, from Sumatra to Celebes, the specimens from 

 Bourbon and Mauritius appruach very nearly to the Malasian specimens : the third 

 form is rare and appears to occur in a sporadic manner in the Philippine Islands 

 and the islands of the Malay archipelago. The fourth form is found in Africa 

 and Southern Europe. 



The forms may be thus defined : — 



First, or east Asiatic form ; moderate size, rather narrow and little convex form, 

 sexual sculpture of the females either fine or entirely wanting ; and the patches of 

 sexual pubescence on the intermediate tarsi of the male are rather narrow, that on 

 the second joint especially being narrow, much narrower than that on the basal 

 joint. 



The second or archipelagic form, is usually of rather broader, more robust and 

 more convex form, the sexual sculpture of the females is very variable indeed, either 

 entirely wanting or largely developed, and the patches of sexual pubescence on the 

 male middle tarsi are broad, that on the second joint being scarcely larger than 

 that on the first. 



The third or sporadic form is of large size, broader behind the middle than the 



