442 Mr. H. J. Carter on the Lithisticke. 



seeing that this, as well as his figure (op. tit. pi. iii. fig. 8), 

 has a discoidal head so deeply fissured as to merit the term 

 mentioned — we seem to have in the surface-spicule a transi- 

 tional form from the three- flat armed head of that in 

 MacAndrewia azorica to that of the subcircular form in the 

 following species, viz. Dactylocalyx polydiscus, where the 

 discoid head is so little fissured as to merit this designation. 

 How far these forms may run into each other in the same 

 species I am ignorant, as I have only examined D. polydiscus, 

 in which all the heads are subcircular. 



Here I should notice that, in a small rolled fragment of 

 Corallistes borealis which I sent to Mr. F. Kitton, of Norwich, 

 to compare with the fossil species to be presently men- 

 tioned, he detected some spicules with subcircular discoid 

 heads, like those of Dactylocalyx polydiscus, which he kindly 

 mounted and sent to me ; and on them I observe two or three 

 of the minute flesh-spicules common to D. polydiscus, but 

 reduced by the process of absorption which takes place in the 

 deciduous vitreous structures of sponges, to be described 

 hereafter, to irregular stick-like forms. Now it so happens 

 that with Schmidt's fig. 8 of the surface-spicule of Corallistes 

 polydiscus there are also two of these irregular stick-like 

 forms represented, which I never could understand until 

 Mr. Kitton sent me the mounted specimen mentioned. Hence 

 it seems to me, from their imperfect form, that Schmidt's 

 minute or flesh-spicules at least belonged to a deciduous 

 skeleton. 



As just stated, the heads of the surface-spicules in Dactylo- 

 calyx polydtscus are discoid and subcircular. The shaft is 

 short, smooth, and pointed ; and where it joins the disk a tri- 

 radiate line is seen, which results from the division of the cen- 

 tral canal of the shaft into three branches. The discoid heads 

 as usual overlap each other ; and the dermal sarcode is charged 

 with the minute flesh-spicule already mentioned ; while in the 

 interspaces between the heads are the pores. The triradiate 

 line is often seen in this kind of spicule in the Lithistidaj, 

 where also the minute, acerate, fusiform, microspined flesh- 

 spicule is also very common. 



In Azorica Pfeiff'erce, n. sp. (two specimens, called after 

 Madame Ida Pfeiffer, who obtained them at Madeira and pre- 

 sented them to the British Museum), the surface-spicule is like 

 that of the interior, viz. with the sinuously branched arms and 

 shaft all terminating in filigreed structure, that of the shaft 

 interlocking with that of the heads of the next layer inside it. 

 There is no very minute flesh-spicule, but a great number of 

 long, subspinulated, fusiform, linear ones, which abound 



