1889.] REV. O. p. CAMBRIDGE ON NEW ARANEIDEA. 3& 



lichen (?) growth that is common on dry soils at this time of year. 

 As seen from above, the door is a square, with its two anterior angles 

 rounded off, the straight side or base forming the hinge-end. But 

 if the door is opened and viewed from below, it lias a circular 

 appearance, reminding one of a gun-wad, which is due to its white 

 lining having been worked into a circular form to fit the mouth of 

 the cyhndrical burrow. In cross section the door is conical, like a 

 plug, with its lower surface convex, like the bottom of a decanter- 

 stopper. This surface is beautifully worked over with a network 

 of fine, toui;h fibres, into which the spider (as I have seen) inserts 

 its claws to keep the door closed against the entrance of an enemy. 

 In no other part of the burrow-lining is this network of fibres to be 

 seen. The door is always made thin at the hinge-end, and thick at 

 the forward end, the average respective thicknesses being one 

 sixteenth of an inch and one quarter of an inch ; so that its section 

 is wedge-like. The result of this construction is that the door will 

 always on release after being opened fall down by its own weight, 

 fitting with exceeding and surprising accuracy into the mouth of the 

 burrow. So prejionderatiiig is the weight of the door at its forward 

 end, and so instantaneously does the actiun of gravity cause it tn fall 

 when released after being held up, that the shutting of the door 

 closely simulates the action of a spring, and it is very difficult at 

 first sight to realize that no elastic force exists in the action. Thus, 

 when a spider sitting at the mouth of its hole, with the door ajar, 

 vesting on its back, darts down its burrow when startled, the door 

 seems to snap down with the action of a suddenly released spring ; 

 but that this is really caused by gravity anyone may convince 

 himself by cutting the mouth of a burrow out of the ground, and 

 noticing the action of the door and its hinge when held upside down. 

 " The hinge, which is beautifully flexible, is formed by a prolonga- 

 tion and local thickening of the lining of the burrow, which is also 

 carried over the lower surface and round the edges of the door. 

 The part cf the lining forming the hinge is thick and tough, and of 

 the same colour outside as the ground, but there is nothing special 

 or mechanical in its structure as a hinge. It may be mentioned here 

 that the lining of the tube is thinned off at the mouth of the 

 burrow to receive the door, a distinct rim being usually observable 

 at the commencement of the burrow proper. There are generally a 

 few withered grass-blades worked into the edge of the door, or into 

 the edge of the mouth of the burrow, so as to form a kind of semi- 

 circular fringe, w hich often catches a practiced eye and leads to the 

 detection of the hole. The grass-blades are probably inserted to aid 

 in assimilatir.g the outside of the burrow to its surroundings, a 

 purpose in which they certainly fail, so far as the hunian animal is 

 concerned. In a few cases I have also noticed grass-blades worked 

 into the general surface of the door, and at this season, when the 

 grass is everywhere withered, these certainly aid in its concealment ; 

 hut during the rains, when the adjacent grass is green, one would 

 think that yellow withered grass-blades on or near the burrow- 

 mouth would tend to make it conspicuous. 



