New Genus of Siliceous Sponges. 397 
wide. The skeleton of the sponges has the appearance in 
thin sections of a minute stellate network, the central nodes 
rounded or slightly elongate, from 0,11 to 0.17 mm. in thick- 
ness ; the spicular rays are about 0.3 mm. in length and 0.03 
in thickness; there are from three to six radiating from 
each node, but they cannot in all cases be traced to their 
union with the proximate nodes. In some cases the spicu- 
lar rays radiate from a non-inflated centre and are thus of 
a tetracladine type; such forms however appear to be ex- 
ceptional. 
This species appears to be not uncommon. The speci- 
mens are all alike in their unfavourable condition of preser- 
vation. In several, the cloaca and main canals have been 
partly filled with microscopic crinoidal joints. 
Distribution. Trenton Limestone, Ottawa. Collected by 
Mr. W. R. Billings, after whom the species is named. 
STELIELLA CRASSA, sp. n., pl. Figs. 5-6. 
The single specimen referred to this species is funnel- 
shaped, with an oblique summit and thick rounded margins. 
The basal extremity is obtusely rounded. The cloacal de- 
pression appears to be shallow. There are only a few traces 
of canal apertures on the outer surface, they are about 1 
mm. in width, their arrangement cannot be ascertained. 
The specimen is 65 mm. in height, and 30 mm. in thickness. 
The large canals are about 1 mm. in width, those of the 
smaller series vary from 0°25 to0.5 mm. wide. The spicular 
structure is of the same character as in the preceding species, 
but the rays of the spicules are decidedly larger, ranging 
up to 0.5 mm. in length, and the spicular mesh is thus of a 
more open character. 
The specimen is in the same state of preservation as tho 
forms described above. 
Distribution. Trenton Formation, Ottawa, Collected by 
Mr. W. R. Billings. 
