Description of new Lower Silurian Sponges .— Ulrich. 237 
small portion of the dermal layer is represented, being really the basal 
part of the sponge. 
Fig. 8 represents a small portion of a transverse fracture of the 
specimen of Streptospongia labyrinthica described; nat. size. 
Fig. 9, portion of the fractured smaller end of the type specimen of 
Oylindrocoslia elongataVl., showing thickness of sponge wall and ra¬ 
diating canals. 
Fig. 10. Outer surface of same, showing distribution of canal aper¬ 
tures when the dermal layer is removed. Both of the natural size. 
RATJFFELLA FILOSA, n. sp. 
Sponge forming a straight or slightly curved hollow cylin¬ 
drical stem, 10 to 15 mm. in diameter. The largest fragment 
seen is 90 mm. in length. One of the ends (whether the 
upper or lower one has not been determined) is rounded off 
somewhat like the tip of a finger. The other, probably, was 
open. Sponge wall less than 0.5 mm. in thickness. Outer 
surface generally appearing to the naked eye as strongly 
striated longitudinally. Under a good pocket lens numerous 
connecting filaments are noticeable forming with the stronger 
threads an irregular, narrow-meshed network. Nearly every 
specimen, however, exhibits on limited portions of the surface 
a comparatively regular arrangement of the spicular tissue in 
diagonally intersecting lines. Here the hexactinellid charac¬ 
ter of the spicules is determined, there being, apparently, four 
rays spread horizontally and one extending downward into the 
inner tissue, while the sixth is not developed. The spicules 
are joined together by a union of the horizontal rays of each 
with those of four other spicules in such a manner that a net¬ 
work with rhomboidal meshes is formed. Similar but smaller 
spicules are developed in the interspaces. This regular ar¬ 
rangement of the spicules is but rarely met with, the surface 
appearing, as already stated, usually to be striated in a longi¬ 
tudinal direction mainly. On an average eleven of the striae 
occur in 5mm. transversely. 
Inner layer of sponge tissue exceedingly thin and minutely 
porous. Its structure has not been determined, the finer de¬ 
tails having been obliterated during the process of fossiliza- 
tion. 
This sponge cannot be confounded with any other fossil 
known to me from Cambrian or Silurian rocks, its finger-like 
form and the strong thread-like striations of the surface giving 
it a very characteristic and easily recognized aspect. 
Formation and locality : Fragments are not uncommon in 
