of Sarcohexactinellid Sponge. 177 



spicules, varying in length from two lines to more than half 

 an inch," resemjjling " the letter X in shape, four of the rays 

 being always very distinct and disposed iu that form ; but 

 [the author continues] there also seems to have certainly been 

 one similar ray extending upwards and another downwards 

 from the centre, considering the other four horizontal ; the 

 rays are round and tapering, smooth and apparently hollow." 



Hence there is nothing more to be learnt from this descrip- 

 tion than that the fossil was part of a hexactinellid sponge ; 

 while among the specimens sent me formerly by Dr. J. Millar, 

 and lately by Mr. Thomson, there are the hexactinellid spicules 

 pf the body in situ, the long, linear anchoring spicules, in at 

 least three specimens of the " lash " or " glass cord," in sitUy 

 and fragments of the fluked ends of the anchoring spicules of 

 the same "lash" probably, but separate] so that in these 

 we have distinctly all the skeleton-spicules that a hyalonema- 

 tous sponge could present, excepting the flesh-spicules, which 

 we do not expect to find here any more than in any other fossil 

 sponge, they, from their extreme minuteness, not being able to 

 survive the effects of fossilization. At the same time it is 

 hardly to be conceived that, if one species of sarcohexacti- 

 nellid sponges existed at this period and in this locality, there 

 were not more ; and therefore the difficulty will be to put 

 those spicules together which originally belonged to the same 

 species. 



Thus we have the undoubted discovery of the fossilized 

 remains of a sarcohexactinellid sponge like Hyalonema from 

 the Carboniferous limestone of " Cunninghambedland, Dairy, 

 Ayrshire," stated by Mr. Thomson to cOme from " the upper 

 thin bed of limestone which is usually found in the upper 

 sections of our lowest Carboniferous Limestone." 



It is probable that both the Acanthasjjongia of M'Coy, de- 

 scribed in 1846, and the Protospongia of Salter, figured and 

 described in 1864, were also the remains of sarcohexactinellid 

 sponges ; while those of the vitreohexactinellids have long 

 since been known, although only just now, in the striking 

 illustrations of Prof. K..A. Zittel, of Munich, and Mr. W. J. 

 Sollas, of our own country, together with their descriptions 

 respectively, brought before the public in the most elaborate, 

 impressive, and satisfactory manner ; but not until now, to 

 my knowledge, have the fossilized remains of a sa/'cohexacti- 

 nellid sponge been thus indisputably proved to exist, and that, 

 too, at a period far antecedent to any of the remains of the 

 vitreohexactinellids hitherto described. 



At first, when Dr. Millar kindly sent me the " hexacti- 

 nellid spicules," they appeared to me, in form and size, to be 



Ann. & Mag. N. Hist. Ser. 4. Vol xx. 12 



