On the Action of Caustic Potash on Sponges. 285 



EXPLAXATIOX OF PLATE VIIL 



Fig. 1. Dictyna boi-ea/is, STp.ii., $: «, profile of ceplialothorax ; 5, fore part 

 of caput and falces ; c, mazillee, labium, aud sternum ; d, spin- 

 ners ; e, natural size of spider. 



Fig. 2. Erigone fVhympcri, sp. n., c? '■ ^» profile without legs ; b, fore part 

 of caput and falces ; c, d, e, palpus of ^ in different positions ; 

 /", genital aperture of j '■> 9i natural size of spider. 



Fig. 3. Erigone arcficci, "White : a, left palpus of cJ , from the outer side ; 

 b, natural length of palpus. 



Fig. 4. Erigone psychrophila, Thor. : right palpus of J, from the inner 

 side above. 



Fig. o. Erigone prorocans, sp. n. : a, spider, enlarged ; b, profile ■without 

 legs : c, left palpus, from beneath on the outer side ; d, natural 

 length of spider. 



Fig. G. Erigone ve.vatrix, sp. n., 5 : «> spider, enlarged ; 5, profile without 

 legs; c, fore part of caput and filces ; d, genital aperture, in per- 

 spective ; e, ditto, in front ; f, natural length of spider. 



Fig. 7. Tai-entula exasperans, s-p.n., $: «, spider, enlarged ; 6, palpus and 

 palpal organs ; c, natural length of spider. 



XXXVI. — On the Changes produced in the Siliceous Skeletons 

 of certain Sponges hy the Action of Caustic Potash. By W. 

 J. SoLLAS, M.A., F.G.S., formerly Scholar of St. John's 

 College, Cambridge. 



[Plate IX.] 



Amongst the variou.s problems which have arisen in the diffi- 

 cult study of the sponges, that as to the exact nature of the 

 skeletal network of such genera as Farrea^ Dactylocalyx^ and 

 Aphrocallistes has not been one of the most easily solved. 



Bowerbank, who was the first to express an opinion on the 

 subject, regarded the vitreo-hexactinellid network as the exact 

 representative amongst the Silicea of the horny network of the 

 kerataccous sponges. In the latter he had previously distin- 

 guished two marked types — one in which the horny fibres are 

 solid throughout [Spongia officinalis) , and another in which the 

 axis of the fibre is occupied by a hollow canal ( Verongia). The 

 same difference he now stated to exist amongst the siliceous- 

 netted sponges, and upon it separated the genera Dactylocalyx^ 

 Iphiteon, and Myliusia, the fibres of which he regarded as 

 solid, from certain other genera {Kaliapsis, Farrea, and Puri- 

 siphonia) , which he considered to possess canaliculated or " fis- 

 tulose " fibre. The interpretation next advanced appears to 

 have originated with the late Dr. Gray, and was adopted with 

 wider application by Professor Sir Wyville Thomson *, who, 



♦ 'Annals and Magazine of Natural History,' Februaiy 1868, p. 114. 



