196 BRITISH JURASSIC SPONGES. 
them are from 1 mm. to 2 mm. in thickness. The spicular mesh, as seen in thin 
sections (Pl. X, fig. 1 a) is lax and irregular, bounding very unequal interspaces. 
One of the largest fragments met with, figured on Pl. X, fig. 1, appears to be 
the upper portion of a large cup-shaped specimen, probably 150 mm. in diameter. 
Smaller fragments are not at all uncommon, but they are all in very unfavorable 
preservation ; usually the ostia of only one surface are exposed, whilst the spicular 
structure is invariably replaced by calcite and very imperfectly shown. In the 
size and arrangement of the ostia the specimens resemble some fragments from 
the Upper Jura, which have been figured by Quenstedt as portions of 
Tremadictyon reticulatum, Goldf. (‘ Petrefactenkunde Deutschlands,’ pl. exv, figs. 14, 
27), but it may be doubted if these really belong to the same species as Goldfuss’s 
type. Further, the spicular mesh in the fragments from the Inferior Oolite 
(Pl. X, fig. 1 a), appears distinctly more irregular than in T. reticulatum from 
the Upper Jura of Germany, of which a small piece is figured for comparison 
(PIE XS fig. 3). 
Distribution.—Inferior Oolite. Parkinsoni-zone at Burton Bradstock, near 
Bridport, Dorset (Walton Coll., Woodwardian Museum, Cambridge). 
2. 'TREMADIOTYON INcERTUM, Hinde, sp. nov. Plate X, figs. 2, 4. 
Cup- or funnel-shaped sponges with thick walls ranging from 18 to 30 mm. in 
thickness ; the ostia of the outer surface are oval in form, and from 2 mm. to 
4 mm. in diameter. The spicular mesh is very irregular and open. Fairly 
complete examples as well as large fragments of this species are known, but both 
the canal and spicular structures in all of them are now so indistinct that it is 
difficult to determine whether they properly belong to this genus or not. 
The most complete specimen (Pl. X, fig. 4) is funnel-shaped, 125 mm. in 
height, by 90 mm. in width at the summit. Near the upper margin there are a 
few oval ostia shown, which appear to have been disposed closely in alternate 
rows; the rest of the surface is unevenly weathered, and no dermal layer is 
preserved, though in some places the irregular mesh of the skeleton can be seen. 
In sections of the sponge wall the spicular skeleton appears as an irregular 
network with very unequal meshes ; the nodes are compact, but there are small 
apertures in some of them arising from the unequal deposition of the silica near 
the nodes. The canal structure cannot be made out with certainty. The interior 
of the sponge has been completely filled with the matrix of calcareous ooze, and 
the skeleton has been wholly replaced by calcite. 
Distribution.—Inferior Oolite. Parkinsoni-zone in the Cliff-section at Burton 
Bradstock, Dorset. (Coll. G. J. Hinde.) 
