so-called "Farringdon Sponges." 33 



alluded ; and the colossal size of the axial spicule has been 

 most faithfully described and portrayed by Dr. Ilinde (/. c. 

 No. 14), — all of which led me to ask myself if I could not find 

 some lingering existence of it in existing species, when I remem- 

 bered that I had by me a little Australian Calcisponge that 

 had, from its peculiar spiculation, been put by for opportune 

 description. On turning to it I observed that its spiculation, 

 although not identical with that of Sestrostomella^ neverthe- 

 less presented the same principle; that is, it consisted of 

 comparatively colossal triradiates of a peculiar form, covered 

 * in by much smaller equiarmed ones of the staple kind. This 



species, as it is new, I will describe under the name of 



Leucetta datlirata^ n. gen. et sp. (PL I. figs. 13-17.) 



Small, flat, sessile, cake-like in form, more or less subcir- 

 cular, slightly convex (PL I. fig. 13, a). Texture firm. 

 Colour now light yellowish white. Consisting of a fibro- 

 clathrous spicular structure which, spreading upwards from a 

 continuous layer adherent to the frond of the foliaceous coral- 

 line (Udotea, sp.) on which it has grown, terminates above 

 in a free surface that presents a solid vermiculo-reticulation 

 in prominent relief (fig. 14), of which the interstices commu- 

 nicate with the clathrous structure throughout, while the 

 summit is devoted to the osculum (fig. 14, a), which is but an 

 enlarged interstice of the vermiculo-reticulated surface, the 

 rest in the fresh state probably having been covered by a 

 thin layer of dermal sarcode in which the pores or inhalant 

 orifices were situated. Spicules all triradiate, but of two dis- 

 tinct forms, viz. : — one of great size comparatively, consisting of 

 three stout arms of equal length and thickness, bent down- 

 wards from a dome-like summit and everted at the extremities 

 so as to form a kind of tripod, averaging in its largest size 

 about 31-6000ths inch high and 38-6000ths inch at the base, 

 with a thickness of 9-6000ths inch in the largest part of the arms 

 (fig. 16) ; the other much smaller, consisting of an equiarmed 

 equiangled triradiate, averaging in its largest size about 18- 

 6000ths by 2i-6000ths inch in the greatest dimensions of its 

 arms (fig. 1 7) . The former, few in number comparatively, are 

 confined to the free surface, where their summits alone are 

 chiefly visible (fig. 15, a a) along the lines of the vermiculo- 

 reticulation, while their arms, being directed inwards, are 

 concealed by the smaller triradiates which in infinitely greater 

 numbers form the rest of the structure, and thus echinate the 

 surface with their projecting rays (fig. 15, c c). Size of largest 

 specimen about 2-12ths inch in diameter by 1-48 th inch in 

 thickness. 



Ann. & Mag. N. Hist. Ser. 5. Vol. xi. 3 



