PHORMOSELLA. 125 



other four in the plane of the wall. It is very likely that rod-like spicules may 

 also be intermingled with the cruciform and five-rayed spicules. 



The type-specimen is in the collection of the Geological Survey of Scotland, 

 Edinburgh. 



Distribution. — Silurian : Upper-Ludlow strata ; Wetherlawlinn, Pentland Hills, 

 near Edinburgh. 



Genus. 1 — Phormosella, Hinde, gen. nov. 



Generic Characters. — Spherical or sacciform Sponges, apparently free. The 

 skeleton consists of a delicate wall of spicular tissue, composed of cruciform 

 spicules, so disposed that their rays mark out sub-quadrate areas, which are filled 

 in with smaller spicules so as to form a connected meshwork. 



This genus is proposed to include some small Sponges which are preserved as 

 compressed oval markings on the surface of a slab of arenaceous rock. Only the 

 impressions of the spicules in iron-peroxide are shown ; their arrangement differs 

 from that in the allied genus Protospongia, in that there is only a single series of 

 squares in which the smaller spicules are somewhat irregularly disposed. The 

 larger spicules are not grouped in bundles as in the vertical series of Plectoderma 

 and in Dictyophytofi, but they are disposed singly, so that their rays overlap and 

 form vertical and transverse lines. 



10. Phormosella ovata, Hinde, sp. nov. Plate III, figs. 2, 2 a, 2 b. 



The Sponges are circular or oval in outline, without trace of a stem or point of 

 attachment. They vary from 12 to 17 mm. in diameter. No summit-aperture is 

 perceptible, since all the specimens appear to have been compressed laterally so 

 that they are now mere films on the rock-surface. The rays of the larger cruci- 

 form spicules, which mark the sides of the squares, are from 2 to 3 mm. in length. 

 The spicular axes, though generally longitudinal and transverse with respect to 

 the Sponge, sometimes diverge slightly, so that the vertical and horizontal lines 

 are not always strictly continuous. The smaller spicules of the skeleton are very 

 indistinctly seen ; they do not exhibit any regular arrangement. In some specimens 

 there are minute punctate elevations and depressions, probably indicating a fifth 

 ray in some of the spicules. 



1 (j>opfi6s, anything plaited, dimin. 



R 



