58 Dr. G. J. Hinde—A New Ordovician Sponge. 
same features likewise differentiate it from Plectoderma, Hinde, and 
Phormosella, Hinde. 
Patmosaccus Dawsonl, sp. nov. (PI. IV.). 
Sponge of large size, apparently cylindrical in its complete form ; 
the part preserved consists of a flattened portion of the wall-surface 
more than a foot in diameter; both the upper and the basal portions 
of the sponge are wanting. ‘The rhombic meshes of the wall vary 
from 14 to 20 mm. in width, the average width is nearly 17mm. 
The strands of the mesh mostly consist of very slender rod-like 
threads apparently simple, which are loosely arranged, generally 
parallel with each other. At the angles of the mesh there are, very 
frequently, if not in all cases, stouter cruciform, or perhaps five- 
rayed spicules, and slender cruciform spicules are likewise inter- 
mingled with the rods in the strands. In the interstices of the 
mesh-work, and apparently exterior to it, there is, in some portions 
of the sponge, a thin open layer, composed of slender rods and 
cruciform spicules, overlapping each other without definite arrange- 
ment. It is possible that this layer may have formed the outer 
surface of the sponge, for the spicules are of the same character as 
those of the strands of the mesh, but on this point there is some 
uncertainty, for the interstices in some parts of the wall are now 
quite open, and without this spicular layer. 
Some uncertainty also arises respecting the anchoring appendages 
of the sponge, since the basal portion is wanting, and no anchoring 
spicules are found in immediate contact with the specimen, but on 
the surface of the same rock-bed in which it occurs, there are some 
peculiarly ornamented spiral rods which may belong to this species. 
Sir J. W. Dawson has given a diagrammatic representation of one 
of these spicules (op. cit. p. 49, fig. 20) which appears as if it con- 
sisted of several very minute filaments spirally twisted together, like 
the strands of a rope. Hach filament has a row of projecting tuber- 
cles which in the rod are definitely arranged in quincunx, so that 
the general ornamentation is very striking. At the distal end the 
rods are slightly curved, and the raised lines are straight instead of 
spiral. As with the other spicules, these anchoring forms are now 
of pyrites, and it is not easy to decide whether they result from the 
amalgamation of slender strands or whether the spiral tuberculated 
ridges are merely the surface ornaments of a single rod-like spicule. 
Be this as it may, we cannot as yet state positively that these peculiar 
anchoring spicules really belong to the present species. 
So far as can be at present determined this sponge appears to have 
consisted simply of a delicate thin sack or cylinder of spicular strands 
forming a rhombic mesh, with possibly a thin outer spicular layer. 
There is no evidence that the sack inclosed an inner spicular tissue, , 
and probably this thin wall represents its entire skeleton. A similar 
condition seems to have been present in Protospongia, Cyathophycus 
and probably also in Dictyophyton and the genera allied to it, but in 
none of these do we find the structure on such a large scale as in 
the present form. 
