IN JAVA. 119 



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



(Extracted from TIic Proc. ZooJ. Soc, 1884, p. I'JG et sejq.) 



V 



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

 Society, 1883, p. 580J under the provlsioua! 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 dropjiings of a bird ; and it 

 is still more remarkable from the increased reseml)!ance added in the 

 spinning of a thin white web on the surftice 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. Torbes kindly sent me the spider for 

 examination before writing an account of its habits. I immediately 

 lecognised its near affinity to an East-Indian spider (TJiomisus taherosus^ 

 BL), of which I j^ossess 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 comi^letc 

 examination since made has convinced me that these latter species 

 (referred to by Mr. Torbes) 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 Jhomisus tuberosus,, Bl., I have ventured to found a 

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

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

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

 to tliat sj^ider, but also, I have little doubt, to other closely allied 



species.* 



In his description of the habits of T, decipiens, ]\rr, Forl>es expresses 



the difficulty he has in understanding the formation by the spider of a 

 Avcb which, while serving to attach itself to the leaf, at the same time no 

 exactly represents the fluid portion of abird's-drapping spread out on the 

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

 me to imply the conclusion that the spider consciously supplements the 

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

 creta, by spinning a web to resemble the fluid portion. It sccm^ to me, 

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

 natural selection, without suppo=ing consciousness in the Fpidcr in any 

 part of the process. The Aveb 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 resemble the more fluid parts of the excreta, would gradually 

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

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

 same law, more and more like the solid portion. 



* DoleschaU (*TweedeBiidra:2:c tot do Kennid der Araclmiden van den In- 

 dischen Archipel/ p. 58, pi. xi. figs. 9 and 9a) describes and figurci, also from Java, 

 a spider (rAom?su8 dissmills, Dol.) possibly of this genus, and perliaps nearly 

 allied to T. decipiens; but the description is too meagre an:l general to enable 

 any certain conclusiou to be d^a^Yn from it;, an- 1 the figure given of the eyes is 

 totally unlike. 



