Hexactinellidae and Lithistidae. 445 



lastly, a description of the deciduous skeleton of Farrea occa, 

 and the destructive changes which take place in the sponge- 

 spicule generally, followed by the absorbing process in the 

 vitreous fibre of the deciduous Hexactinellidae to which I have 

 often above alluded. 



Short Descriptions of Specimens that will presently 



COME under reference. 



The first of the specimens that came under my observation 

 in this respect was one of the so-called Farrea occa, which, 

 having grown upon a branched coral {Lophokelia prolrfera), 

 subsequently became overgrown, both sponge and coral, by a 

 Oummina [Corticium ahyssi), so as to form a solid mass, 

 through whose smooth surface here and there projected portions 

 of both sponge and coral. This specimen, I learn from the label 

 on the glass jar containing it, was dredged up on board H.M.S. 

 ' Porcupine,' in lat. 43° 31' N., and long. 10° 3' W. (that is, 

 in the so-called "cAo^s" of the English Channel), in 500 

 fathoms. It is now an oblong portion, in size about 2^ x 1^ x f 

 inch, which originally must have been larger, as there are 

 many fragments of it in the same jar. The specimen is figured 

 in the '■ Annals ' for July 1873, pi. i. figs. 1 & 2, of the natural 

 size ; and to this specimen or figure I shall often have to allude 

 as " No. 3 a," which heads the label on the jar. All this may 

 seem unnecessarily particular ; but as the specimens of Spon- 

 giadse dredged up on board H.M.S. 'Porcupine' have been 

 handed over to me by Prof. Wyville Thomson for description, 

 every thing that tends to point out their history should be 

 recorded. 



By the term " so-called i^arrea occa," I mean that this name 

 was given to a simple fragment of vitrified network, found in 

 great abundance in the detrital mass on which Dr. Farre's 

 specimen of Euphctella cuciimer had grown. " Simple," because 

 the fragments are those of dead sponges, and therefore without 

 sarcode, while the minute spicules which accompanied them, 

 and are figured by Dr. Bowerbank as the " retentive spicules " 

 of Farrea occa {I. c), are not those of a sexradiate sponge, 

 which the fragments are, but of an undescribed species of Oum- 

 mina. How far the form and structure of this sponge, to which 

 the fragment figured by Dr. Bowerbank (fig. 7, I. c.) belonged, 

 has been subsequently discovered, the sequel of this paper will 

 show. Sufiice it now to state that we shall take as the cha- 

 racteristic feature of Dr. Bowerbank's Farrea occa the rectan- 

 gular latticed " harrow-like " structure of his illustrations 

 [l. c. pi. xxiv. fig. 7, 1869), first represented by Prof. Owen 

 in connexion with EvplecteUa cucumer (Trans. Linn. Soc. 1857, 



