ELASMOSTOMA PALMATUM. 243 
Genus.—Etasmostoma, Fromentel. 
1859. Introduction 4 1’étude des Eponges fossiles, Mémoires de la Soc, Linnéennede 
Normandie, vol. xi, p. 42. 
Syn.—Tragos, Manon, Spongia, Auct. (in part) ; Porostoma, Chenendroscyphia, 
Fromentel (in part); Chenendopora, Cupulospongia, Roemer (in part); Trachy- 
penia, Coniatopenia, Pomel. 
Sponges with laminated walls, flattened or convolute; occasionally cup- or 
funnel-shaped. One surface of the wall is covered with a smooth, compact, or 
minutely perforate dermal layer, in which are large circular or irregular oscular 
apertures, which open into the interspaces between the skeletal fibres. The 
opposite surface is without a dermal layer, and the fibres are uncovered. Skeletal 
fibres stout, forming an openly reticulate mesh, in which canals, as a rule, are not 
definitely shown. They consist of large axial three-rayed spicules, enclosed by 
sinuous filiform spicules; tuning-fork spicules are likewise present in some 
species, the same as in Holcospongia. 
The type-species is H. acutimargo, Roem., sp. (‘ Verst. d. Nordd. Oolithgeb. 
Nachtrag,’ p. 10, pl. xvu, fig. 26), from the Neocomian at Berklingen, Brunswick. 
51. Eiasmostoma patmatum, Hinde, sp.nov. Plate XVII, figs.9—9c; Plate XVIII, 
figs. 1, la. 
1854. Sponerta HELVELLOIDES, Morris (non Lamx.). Cat. Brit. Foss., 2nd ed., p. 30. 
Sponges growing in the form of fan- or ear-shaped plates, variously curved 
and thickened, attached directly by the margin or by a short blunt pedicle. The 
walls are from 3°5 mm. to 7 mm. in thickness. The dermal layer covering one 
surface is compact, with numerous subcircular or irregular oscules from 2 mm. to 
3 mm. in width, and usually with elevated margins (Pl. XVIII, fig. 1). Some- 
times the oscules are nearly close together, at others about their own diameters 
apart; they open directly into the interspaces of the fibres beneath. The opposite 
or non-oscular surface of the sponge has only the irregular spaces between the 
fibres, which are unusually stout on the exterior (Pl. XVII, fig. 9a). The 
margins of the wall are rounded. 
The skeletal fibres are stout, reticulate, from ‘1 mm. to ‘5 mm. in thickness ; 
the rays of the axial three-rayed spicules range up to ‘26 mm. in length by ‘06 mm. 
in thickness; the smaller sinuous spicules border the fibres, and are interlaced 
