IN JAVA. 119 



n. On a new Genus of Spiders. By Kev. 0. P. Cambridge, M. A., C.M.Z.S., &c. 

 (Extracted from 77w Proc. Zool. Soc, 1884, p. 196 et seqq.) 



Mr. H. 0. Forbes has lately described {Proceedings of the Zoological 

 Society, 1883, p. 580,) under the provisional name of Thomisus decipiens, 

 the habits of a spider which he met with in Java. The spider itself is 

 remarkable from its exact resemblance to the droppings of a bird ; and it 

 is still more remarkable from the increased resemblance added in tho 

 ■spinning of a thin white web on the surface of a leaf, by means of which 

 it secures itself, on its back, to the leaf, leaving its legs free to enclose and 

 seize any insect unwittingly resting upon or crossing Ihe apparantly 

 innocuous bird-dropping. Mr. Forbes kindly sent me tho spider for 

 examination before writing an account of its habits. I immediately 

 lecognised its near afSnity to an East-Indian spider (Tliomisus tuberosus, 

 Bl.), of which I possess the type specimen ; but, unable at the moment to 

 make a thorough examination and search through books and specimens, 

 conjectured that it was allied to some spiders described by Dr. Karsch, 

 and to one sent me some years ago from South Africa.' A more complete 

 examination since made has convinced me that these latter species 

 (referred to by Mr. Forbes) belong to entirely different groups. I find, 

 however, in my collection two other spiders, from Ceylon and Bombay, 

 of the same genus and very closely allied in species, but quite distinct 

 from that which Mr. Forbes notes. Upon these, together with the one 

 last mentioned and Thomisus tuberosus,, Bl., I have ventured to found a 

 new genus, and I beg to record my thanks to its discoverer for so kindly 

 sending mc an example of Thomisus decipiens and for having also made 

 known to us the very peculiar and inleresting habits belonging, not only 

 to that spider, but also, I have little doubt, to other closely allied 

 species.* 



In his desciiption of the habits of T. decipiens, Mr. Forbes expresses 

 the difficulty ho has in understanding tlie formation by the spider of a 

 web which, while serving to attach itself to the leaf, at the same time r,o 

 exactly represents the fluid portion of a bird's-dropping spread out on the 

 leaf around the more solid parts ; and his concluding sentences seem to 

 me to imply the conclusion that the spider consciously supplements the 

 effects of natural selection on its form and resemblance to the solid ex- 

 creta, by spinning a web to resemble the flnid portion. It seems to me, 

 on the contrary, that the whole is easily explained by the operation of 

 natural selection, without 6uppo=ing consciousness in the ppider in any 

 part of the process. The web spun on the surface of the leaf is evidently, 

 so far as the spider has any design or consciousness in the matter, spun 

 simply to secure itself in the proper position to await and seize its prey. 

 The silk, which by its fineness, whiteness, and close adhesion to the leaf 

 causes it to respmble the more fluid parts of tho excreta, would gradually 

 attain those qualities by natural selection, just as the spider itself would 

 gradually, and probably pari passu, become, under the influence of the 

 same law, more and more like the solid portion. 



* Doleschall ('Tweede BiidraQ;e tot de Kennis der Avachniden van den Iii- 

 dischen Archipel,' p. 58, pi. x'i. fi5;3. 9 and 9o) describes and figures, also from Java, 

 a spider ('f/iomisus dissimilis, Dol.) possibly of this genus, and perhaps nearly 

 allied to T. decipiens; but the description is too meagre, and general to enable 

 any certain conclusion to be drawn from it, and tho figure given of the eyes is 

 totally unlike. 



