108 BRITISH PALASOZOIC SPONGES. 
spicular mesh is composed of robust cruciform spicules, the rays are approximately 
rectangular, and nearly of a uniform thickness throughout their length. The 
centres of the spicules are slightly elevated, so that they are not strictly horizontal. 
The rays of the smaller spicules in the majority of cases dip beneath those of the 
larger forms. Five series of squares are present in the complete mesh, the largest 
are 8 mm. in diameter and the smallest °5 mm.; the axes of the largest spicules 
are 16 mm. in length and 52 mm. in thickness, whilst the smallest are 1 mm. in 
length and *2 mm. in thickness. 
The typical example of this species, now in the Woodwardian Museum at 
Cambridge, is preserved on a block of black slate. The spicular mesh has been 
replaced by iron-pyrites; in places it stands boldly out from the rock surface. 
Though the regular arrangement of the spicules of the mesh is clearly shown in 
only one portion of the specimen, it can be traced over an extended surface, and it 
occurs at two different levels separated by an interval of matrix, of about 4 mm. in 
thickness. This appears to me to indicate that the entire Sponge was vasiform or 
cup-shaped, and that, owing to pressure, the opposite walls of the cup are now 
nearly in contact with each other. 
The original specimen was discovered by Dr. H. Hicks, F.R.S., who referred it 
to P. fenestrata, Salter. It was subsequently described in considerable detail by 
Prof. Sollas, who also regarded it as identical with Salter’s species. A comparison 
of this form with the type of P. fenestrata shows, however, a very considerable 
difference in the thickness of the spicular rays, sufficient to indicate it asa distinct 
species, which I have named in honour of its discoverer. 
In no case in this specimen are the points of contact of the spicules with each 
other clearly shown, but the structure of the mesh appears to me to justify the 
view that the spicules are cemented together where they join each other; Prof. 
Sollas states, however, that they are separated and not united either by envelop- 
ment in a common coating or by ankylosis. 
Fragments of mesh and detached cruciform spicules, apparently belonging to 
this species, have been discovered in Norway, Sweden, and also in Nevada, at 
approximately the same geological horizon. 
Distribution. —Cambrian ; Menevian Group. Porth-y-Rhaw, near St. David’s, 
South Wales. Cambrian; Paradoxides-Shales, Krekling, Norway (Brégger) ; at 
Andrarum, Sweden, in beds with Paradowides and Agnostus pisiformis; Eureka 
district, Nevada, in the Prospect Mountain Group (Walcott). 
