238 Description of new Lower Silurian Sponges — TJlrich. 
the Trenton shales at Minneapolis, St. Paul, Fountain and 
other localities in Minnesota. 
RATJFFELLA PALMIPES, n. sp. 
Sponges rather large, originally probably of inverted pear- 
shaped outline, consisting of five bi- or tri-furcating com¬ 
pressed lobes springing from a short stem, united at the cen¬ 
ter and arranged in a radial manner. In the fossil state they 
present varied forms corresponding with the degree and direc¬ 
tion of the compression they have suffered. This is much less 
than might be expected of so frail an organism, and I can ac¬ 
count for the comparatively good preservation of the shape 
only by supposing the lower extremity of the stem to have 
been open, thus permitting the material that made up the 
strata (mud, fragments of shells, bryozoa, etc.) to enter freely 
into the internal cavity. Generally, the cavity is entirely 
filled with material of the same nature as the surrounding 
matrix. In a few cases free communication must have been 
interrupted causing a lobe to remain empty and now to appear 
much more compressed than usual. On account of the friable 
nature of the shales in which they are found, most of the spec¬ 
imens are mere fragments. Still after a careful search the 
author succeeded in securing three nearly complete examples. 
Two of these are compressed obliquely with the stem on one 
side, and look very much like the webbed foot of a bird. The 
specific name was suggested by this fancied resemblance. The 
third is compressed vertically and shows the radial arrange¬ 
ment and bifurcation of the compressed lobes very satisfactor¬ 
ily. As near as can be determined the original dimensions of 
a specimen of medium size were about as follows : hight, 90 
mm.; greatest width, 80 mm.; diameter of stem, 15 mm. ; 
thickness of lobe, 8 mm.; thickness of walls of sponge, 0.5 
mm. or less. 
The spicules of the inner layer, owing to alteration and re¬ 
placement by calcite, have not been determined. A thin sec¬ 
tion, however, shows that it was minutely porous, the tissue 
separating the pores thin, and the pores of variable size, the 
larger ones of rounded form, the smaller ones more or less 
angular. The surface, as in B. Mosa, is striated, only the 
striae are much finer and more irregular. The appearance of 
the surface is to be described as hirsute rather than filose. 
