On Aquatic Carnivorous Coleoptera or Dytiscidce. 721 



1133. Cybister binotatus, Klug, Tragus hinotntus M.C. — Ovalis, parum latus, 

 convexus, supra olivaceo-niger, prothoracis lateribus plus minusve obsolete rufes- 

 centibus, elytris versus apicem ssepius rufo-notatis, subtus niger, pedibus nigricanti- 

 bus, anterioribus et intermediis plus minusve rufo-variis, antennis rufis, extrorsum 

 parum fuscescentibus : epipleuris angustis. Loug. 28, lac. 15 m.m. 



The male in this species has the front tarsi rather large in the transverse direction, 

 but the pubescent area beneath remains small ; the intermediate tarsi have on the 

 basal joint a rather large patch of rather short hair, this patch has the form of a 

 narrow triangle ; there may sometimes be a very slight development of sexual 

 liairs also on the following joint. The female has always some sexual sculpture on 

 the elytra, though sometimes it is excessively scanty, while sometimes there is 

 even a highly developed sculpture on the thorax, and in the most extreme cases 

 also on the head. 



The species is a very variable one, and four forms may be distinguished as regards 

 the female sex, although the corresponding males can scarcely or not at all be sepa- 

 rated from one another. First there is the African form ; the female of this has some 

 short, isolated scratches on the middle of the elytra in their basal portion, these are 

 variable in their number and extent, and in the most advanced cases they extend 

 from the scutellum to the shoulder and one half of the length of the elytra, the 

 sutural portion of the elytra remaining smooth however through nearly its whole 

 lensfth ; in these extreme cases there are even a few fine scratches on the basal 

 portion of the thorax. 



The second form of the female is found in Madagascar, and is the Cybister 

 madagascariensis of Aube ; in this the sexual sculpture is usually greater, and 

 extends more on the anterior part of the insect, the scratches on the elytra are in 

 the least sculptured specimens very few, but they are then placed more on the 

 basal and humeral portion of the elytra, than in the corresponding slightly sculptured 

 individuals of the first form, and there are always fine scratches on the sides of the 

 thorax and one or two behind the eye ; in the most advanced cases of this 

 Madagascar form, the scratches become a good deal deeper and more numerous, 

 and extend over a similar area to what they do in the first form, the thorax becomes 

 nearly covered with short scratches, and those about the eyes though always fine, 

 are more numerous. 



The third form of the female is that found in Mauritius, (Cyl>ister desjardinsii, 

 Aube), the sexual sculpture seems to be here always (to judge from the few in- 

 dividuals I have seen) highly developed, and extends over two-thirds or three-fourths 

 of the whole area, the sutural portion being much less free from scratches than in 

 the first two forms : the thoracic sculpture is highly developed and beautiful, and 

 quite covers the surface ; on the head there are scratches all along the occiput, and 

 even the central area of the head bears fine scratches. 



The fourth form of the female is that found in Arabia ; the sculpture of the wing 



