4 18 Mr. J. Blackwall on the Structure, Functions, (Economy, 



from Barmouth, in Merionethshire, in the summer of 1835, by 

 Richard Potter, Esq., M.A., of Queen's College, Cambridge, and 

 Professor of Natural Philosophy in University College, London. 

 In 1836 I received an adult male from Mr. T. Glover, which he 

 had taken in Liverpool, and I have in ray possession an im- 

 mature individual from the Isle of Wight. 



The spider referred to by Mr. Jesse in his ' Scenes and Tales 

 of Country Life,' pp. 203, 203, as remarkable for the rapidity 

 of its vibratory motions when disturbed, is, I have no doubt, 

 Pholcus phalangioides, which frequents ancient buildings in the 

 south of England, and like Epeira diadema, Theridion quadri- 

 punctatum, and some other species, has the habit of violently 

 agitating itself when anything suddenly touches its lines. This 

 vibratory motion, which in the case of Pholcus phalangioides ap- 

 pears to acquire its maximum velocity, is produced by the partial 

 contraction and extension of the joints of the legs in quick 

 succession, as I have ascertained by occasioning specimens of 

 Epeira diadema to continue the action till it became so slow, in 

 consequence of the fatigue experienced by the animals, that there 

 was no ditficulty in determining the manner in which it is effected. 

 This singular proceeding is evidently intended by the spider to 

 communicate motion to its snare and thus to cause the struggles 

 of any insect entangled in it, by which means it is directed with 

 certainty to its victim. 



Family Linyphiida. 

 Genus Linyphia, Latr. 

 101. Limjphia montana. 



Linyphia montana, Walck. Hist. Nat. des Insect. Apt. t. ii. p. 233. 

 pi. 16, fig. 4; Koch, Uebers. des Arachn. Syst. erstes Heft, 

 p. 10; Die Arachn. B. xii. p. 113. tab. 422. fig. 1038, 1039. 



triangularis, Latr. Gen. Crust, et Insect, torn. i. p. 100 ; Sund. 



Vet. Acad. Handl. 1829, p. 215. 



This very common spider, which is frequently mistaken for 

 Linyphia triangularis, constructs in hedges, bushes and rank 

 herbage an extensive horizontal sheet of web of a fine texture, 

 on the inferior surface of which it takes its station in an inverted 

 position and watches for its prey. Connected with the web and 

 with objects situated above and below it are numerous fine lines 

 intersecting one another at various angles ; those on the upper 

 side are the most extensive, and not only serve to support the 

 web, but also to precipitate such insects as strike against them 

 with their wings upon the horizontal sheet, where they are 

 quickly seized by the vigilant and active occupant. 



