208 BRITISH JURASSIC SPONGES. 
spicular mesh, which has been replaced by calcite, or in places dissolved away, 
leaving empty spaces in the matrix, is of a very close character ; in thin sections 
it appears as a very fine reticulation, the nodes being connected by short rays; 
sometimes the meshes are subquadrate in outline. On the weathered surface of the 
sponge the minute spherical nodes of the spicules with their connecting rays stand 
out prominently and can be distinguished under the microscope (PI. XIII, fig. 1 ¢). 
On comparing this structure with that of Melonella radiata, Quenstedt, of which 
there are several specimens in the British Natural History Museum, in the same 
condition of preservation, a very close resemblance is apparent. As in all the 
specimens of Melonella, the spicules in these sponges have been replaced by 
calcite. I have figured two of the siliceous spicules of Cylindrophyma milleporatum, 
Goldfuss, sp. (Pl. XIII, figs. 2, 2a), for comparison with those of the present form. 
This species was described by Prof. Sollas as the type of a new genus of 
Hexactinellid sponges characterised by having a canal system like that of the 
Lithistid genus Siphonia. There can be no doubt, however, that its spicular 
structure is really of the Anomocladina type, and that it is closely related to 
Melonella radiata. The mistake in its identification has arisen from the fact—as 
already remarked by Prof. v. Zittel—that the spicular structure of this group of 
Lithistids has often a deceptive resemblance to that of certain Hexactinellids, and 
more especially is this the case when the silica of the spicules has been replaced 
by calcite. Independently of the spicular structure, the general build and the 
character of the canal system in these sponges are sufficient to betray their 
relationship to typical Lithistids. 
Distribution.—Inferior Oolite. Humphresianus-zone at Dundry Hill, near 
Bristol. (Coll. Rev. G. F. Whidborne.) 
Sus-orpEr.—THTRACTINELLIDA. 
Genus.—PACHASTRELLA. 
16. PacHAsTRELLA aNnTIQUA, Moore, sp. Plate XIII, figs. 3, 4. 
1867. Granrra antigua, Moore. Quart. Journ. Geol. Soc., vol. xxiii, p. 538, 
pl. xvi, figs. 33, 34. 
1878. PacHASTRELLA ANTIQUA, Carter. Ann. and Mag. Nat. Hist., ser. 5, vol. i, 
p- 418. 
1883. = — Sollas. Quart. Journ. Geol. Soc., vol. xxxix, 
p- 542, note. 
1883. — — Hinde. Cat. Foss. Sponges, B. Mus.,p. 209, note. 
Form of sponge unknown; the species is based on detached three- and four- 
rayed caltrop spicules; the rays in a small specimen are °35 mm. in length by 
