

Hexactinellidge and Lithistidas. 471 



Fig. 4. Farrea occa. Fragment of deciduous skeleton from the last-named 

 specimen showing that the smooth, lattice-like, suhrectangular 

 fibre is based on sexradiate spicules, as above mentioned : nana, 

 lattice-like fibre, smooth ; bbb, moulds of sexradiate spicules ; 

 ccc, short conical spiniferous extensions of the fibre, corre- 

 sponding to the two arms of the sexradiate spicule, which pro- 

 jected vertically both inside and outside of the lattice-like 

 structure. Scale l-24th to 1-I800th of an inch. 



Fig. 5. Farrea occa, fragment of, from the same specimen, showing an 

 enclosure of part of a fusiform spined spicule in the vitreous 

 fibre (PI. XV. fig. 8) : a a, smooth vitrified fibre ; b, itwimbedded 

 half of fusiform spined spicule ; c, imbedded half of the same. 

 Scale l-24th to l-1800th of an inch. 



This spicide is common in the Aphrocallistidse, Aulodictyon, 

 &c. 



Fig. 6. Farrea occa, fragment of, from the same specimen, showing the 

 enclosure of a scopuline spicule with pointed rays, like that 

 figured by Schmidt as occurring in his F. facunda : a a, smooth 

 vitrified fibre ; b, mould of scopuline spicule (see a similar form 

 found occasionally in Aphrocallistes Bocagei, PL XV. fig. 3). 



Fig. 7. Farrea occa, fragment of, from the same specimen, showing the 

 enclosure of another form of scopuline spicide with pointed 

 rays ; also a capitate spicule of a larger kind, often observed : 

 a, smooth vitrified fibre ; b, scopuline spicule ; c, capitate spicule, 

 in which the head seems in some instances to be flattened ; the 

 latter is introduced by Schmidt as an arm of a fossilized sex- 

 radiate spicule (tab. ii. f. 18, op. cit.). 



Figs. 6 and 7 are on the scale of l-24th to 1 -6000th of an 

 inch. 



Fig. 8. Fragment of a large deciduous linear spicide (from Geodia?), 

 to show the different forms caused by some eroding organism : 



a, simple circular depression ; b, straight tubular form ; c, the 

 same, expanding into a globular termination in the substance 

 of the spicule. Diagrammatic. 



Fig. 9. The same, more magnified, to show that each of the forms is 

 attended by a granuliferous cell something like the saprolegneous 

 one (Pythiiim entophytum) which bores its way through the 

 cell-wall of Spirogyra, &c. a a a, granuliferous cell. 



Appears to be of general occurrence, as I have specimens 

 from the Agulhas Shoal at the Cape of Good Hope, dredged up 

 by Dr. Wallich, from the dredgings of H.M.S. ' Porcupine ' oft 

 the north coast of Scotland, and from the Seychelles, among the 

 detrital mass of the specimen of EuplecteUa cucumer in the pos- 

 session of Dr. A. Farre, &c. &c. 



Plate XVII. 

 New Species of Hexactinellidse, &c. 



Fig. 1. Farrea infundibidifortnis, sp. n. a, funnel-shaped _ expansion ; 



b, stem ; c, reticulating lines of large, branching, vitreous fibre 

 imbedding minute sexradiate spicules confusedly, fibre micro- 

 spined ; d, distinct or accessory portion of small vitreous fibre 

 imbedding the same regularly; e, dotted line indicative of 

 original expansion. Natural size. 



Fig. 2. The same, portion of inner surface of funnel-shaped expansion, 



