Mr. II. J. Carter on the Antipatharia. 395 



smooth surface and glassy lustre of fresh spicules ; the surface, 

 indeed, differs very much as that of ground from polished 

 glass. That they have exchanged the colloid for the crystal- 

 line state is clearly shown by the elevation which has taken 

 place in their refractive index and by the colours which they 

 give with polarized light. The effects of solution are visible 

 in little hemispherical pits which have been eaten in over the 

 surface (fig. 46) , and by the irregular outline of some of the 

 fusiform spicules, which appear in optical section as though 

 irregularly scolloped. The canals of many are enlarged, but 

 obliterated in the majority, probably as a result of secondary 

 silicification. To secondary silicification we may also refer 

 the tuberculation of some of the forms. Occasionally den-' 

 drites of iron pyrites are seen shooting through the substance 

 of the spicules, the first stage of a replacement which is found 

 completed in spicules from other deposits. 



Probable depth of the Sea. — The sponges which furnished 

 the spicules lived on a sea-floor probably somewhere between 

 100 and 400 fathoms deep. The Lithistida?, which have fur- 

 nished so large a proportion of the spicules, have been 

 dredged from depths varying between 75 and 374 fathoms. 

 Lyidium torquilla, which so closely resembles the fossil 

 Podapsis, was obtained from a depth of 270 fathoms. Of 

 other sponges the recent Pachastrella geodoides, which our 

 P. globiger resembles, was dredged from 292 fathoms, and 

 Geodia Macandrewi, which is represented by the fossil Q, 

 cretaceus, from 100 to 270 fathoms. 



[To be continued.] 



XL VIII. — Additional Observations on the Antipatharia. 

 By H. J. Caeter, F.R.S. &c. 



By reference to the footnote at page 304 of the last number 

 of the ' Annals,' it will be seen that I had not then read 

 Lacaze-Duthiers's memoirs " Sur les Antipathaires " (in the 

 ' Annales des Sciences Naturelles, Zoologie,' tomes ii. and 

 iv. pp. 169 and 1 of 1864 and 1865 respectively) at the time 

 that I finished my short article on the Antipatharia, chiefly 

 questioning the nature of the polyp (viz. whether Hydroid or 

 Actinoid?), and stating, at page 302, that MM. Milne- 

 Edwards and Jules Haime, in 1857, had summed up our 

 knowledge on this point in the following way, viz. : — ■ 

 " Jusqu'ici on n'a pas etudie l'anatomie de ces animaux, et on 



28* 



