226 RECORDS OF THE AUSTRALIAN MUSEUM. 



former has been denned by Simon as " Orbis totius regiones 

 tropica?,"- ,; but it also occurs in .subtropical and, to a limited 

 extent, in temperate zones : the latter genus is only found in 

 " Brasilia : Amazonas." 2 7 



About 200 species of Gasteracantha have been described, and 

 these have been divided by Simon into two sections, based upon 

 the structure of the abdomen, and the number and proportion of 

 the spines, and these include several subgenera. 28 



The Gasteracantha are easily distinguished by the abdomen, 

 which is hard (chiiinous), armed with two, four, or six spines, 

 which vary in length, strength, and direction, and issue from 

 <1 liferent points of the margin The abdomen is also marked on 

 tiie upper surface, and sometimes underneath, with numerous 

 symmetrically disposed cicatrose spots, varying a little in size, 

 form, and position. These markings Cambridge designated 

 sigilla, owing to their resemblance to seals impressed upon the 

 surface. The number, distribution, and relative distinctiveness 

 of these sigilla are often of assistance in the determination of 

 the species. The males are veritable pigmies compared with the 

 females, and differ much from the latter in respect of abdominal 

 armature. In some species of Gasteracantha the abdomen is 

 very flat, in others it is more or less arched, but whichever it 

 may lie it is always very large in proportion to the cephalothorax, 

 and its anterior angle always overhangs the latter. The legs are 

 always short. 



The webs of Gasteracantha are usually constructed in open 

 places. The species common around Sydney, G. minax, Thor,, 

 = G. Jlavomaculata, Keys., constructs a snare about eighteen 

 inches in diameter; it is orbicular, vertical, and closely meshed. 

 The rays vary in number (22 to 30) and do not meet at the centre, 

 but are connected with a common ring. When the web is newly 

 constructed the rays do meet, but the central extremities aie 

 afterwards cut away, thus leaving an open ring or hub. The 

 beaded spirals commence close to the ring and continue towards 

 the outer lines or framework. There is no stabilimentuni present. 

 According to McCook and Simon, some species decorate their 

 webs with tufts of white, flossy silk, but those that I have seen 

 in the bush around Sydney were not so ornamented. The latter 

 author, however, says that the habit is variable with the same 



Simon — Loc. cit., p. 845. 

 - T Simon — Loc. cit., p. s 17. 

 Simon— Loc. cit., pp. 838-843, pp. 845-847. 



