Prof./VV. Thomson on the " Vitreous " Sjionges. 125 



substance, composed mainly of a siliceous tubing formed es- 

 sentially by the coalescence of spicules of the hexradiate type 

 in every condition of distortion, is regularly spread, partially 

 closing and reducing to rounded pores, by an oblique tissue of 

 interlacing threads, the square meshes of the frame, and rising 

 on the surface of the sponge into irregular spiral ridges. 



The mouth of the tube is closed, as in Hahrodictyon corhicula^ 

 by a nettecT lid of dense tissue. Not taking into account dif- 

 ferences in the form of the spicules, of specific value only — if 

 the siliceous coil of Hyalonema were separated into small bun- 

 dles and attached by transverse fibres within the wall of the 

 tube of Hahrodictyon, we should have a Sponge which would 

 be referred without doubt to the genus Eiqilectella. 



AphrocaUistes is very nearly allied to EupJecteUa. There 

 are the same fascicles of longitudinal fibres within the tube, and 

 there is the same netted lid ; but the tube is irregular in form, 

 and the siliceous network is much more dense and compact. 

 It will be remembered that some of the spicules of the sarcode 

 in Aphroccdlistes resemble those in Farrea, while others corre- 

 spond with the form hitherto only known in Dactylocalyx^. 

 In Dactylocalyx the longitudinal fascicles have disappeared, and 

 the siliceous network is much more dense and irregular. A 

 specimen from Barbadoes, which I saw in the Paris Exhibition, 

 had almost the cylindrical form of Aplirocallistes ; an example 

 in the Belfast Museum is cup-shaped and looks like a silicified 

 bath-sponge. I hope to have an opportunity of revising the 

 whole of this genus or group of genera on some future occasion. 

 The ultimate structure of its siliceous network and the close 

 resemblance in form of its sarcode-spicules associate Dactylo- 

 calyx clearly with AphrocaUistes and Farrea. 



Farrea is undoubtedly a vitreous Sponge allied to Aphro- 

 caUistes. The hexradiate type of the framework, and the spi- 

 cules figured by Dr. Bowerbank (Brit. Spong. figs. 199, 200), 

 are very characteristic. I am in doubt about the bihamate 

 spicule {ibid. fig. 114). From the condition of the only known 

 example of Farrea occa, I should think it possible that one or 

 many sj)icules of that form may have been mixed with it, 

 possibly from some associated species of Esperia. 



Eelations of the Group. 

 It is difficult even to speculate upon the position of the 

 vitreous Sponges in the series of the Porifera. There is 



* I am indebted to my friend Dr. Gray for an opportunity of examining 

 the minute structure of Aiihrocallides. The woodcut represents a frag- 

 ment of the general network of the wall of the tube, with some of the 

 characteristic spicules of the sarcode alluded to above. 



Ann. & Mag. N. Hist. Ser. 4. Vol.i. 10 



