HORIZONTAL SCARES AND DOMED ORBS. 



167 



three common variations of the form : First, a plain sheet of thin silk 

 attached to the under part of leaves or suspended between branches as in 

 the webs of Linyphia costata. Second, the snare of L. communis, represented 

 at Fig. 156. It has a mass of right lines, r, to which is suspended a bowl 

 like sheet, b, beneath which again is a dish shaped sheet, d, of more open 

 spinningwork with the concavity upward, as in the bowl. The snare from 

 which this figure was drawn had a total height of from twelve to fourteen 

 inches. The diameter of the bowl was from 

 six to seven inches, its depth one and a half 

 to two inches. 



Linyphia communis hangs inverted to the 

 lower surface of her bowl, and is thus pro- 

 tected from assaults by the underlying floor 

 or dish or curtain, d. 



A third variation is that of the beautiful 

 snare of Linyphia marginata (L. marmorata 

 of Hentz), which is in form precisely like 

 that just described except that the bowl 

 becomes therein a dome. That is to say, 

 the sheet, b, has the concavity downward 

 instead of upward, and the dish or cur- 

 tain undergoes a similar change. In 

 other words, the web of Marginata 

 has the exact form of Basilica's 

 web, except that in the latter the 

 dome, d (Fig. 154), is constructed 

 of open regular meshes formed by 

 the intersection of radiating ribs 

 of silk with notched concentrics, 

 while Marginata's dome is woven 

 of irregularly placed threads into 

 a thin sheeted web. The lower curtains, and the upper retitelarian web are 

 substantially the same hi both. In other words, the typical character of 

 an Orbweaver's snare, namely, regular radiating lines regularly crossed by 

 spiral concentrics, appears in the web of Basilica without any other change 

 from a fixed generic Linyphiau web. In the figure (157) the three netted 

 domes were apparently made successively by one spider, 4 and abandoned 

 for some undiscovered reason. The ordinary web contains only one dome. 

 It is probable that the curtain usually found beneath this is the compressed 

 remains of a former dome, above which a new tent is reared. Something 

 of the same habit may be seen hi certain Orbweavers, who, however, push 

 the rejected material to the outer margins instead of beneath the web. 



We may trace this interesting analogy from another point in the group 

 of Orbweavers, and find yet further coincidence. The typical orb of the 



5-. 



FIG. 157. The snare of Linyphia marginata. 



