Description of new Lower Silurian Sponges .— Ulrich. 239 
Formation and locality: Trenton shales, near Minneapo¬ 
lis, Minn. 
EEPTOPOTERIQN MAMMIFEEUM, n. g-en. et. sp. 
Sponge free, obconical, about 70 mm. high and 40 mm. 
wide at the top. At intervals of about 9 mm. the sides are 
marked with shallow transverse constrictions, giving the 
sponge, particularly the lower half, an annulated appearance. 
The basal portion, which is 14 mm. in diameter at the first con¬ 
striction and 8 mm. high, seems to have formed a nearly hem¬ 
ispherical termination. The second annulation shows seven 
very faintly defined broad elevations ; the third, eight a little 
more distinct; the fourth, nine, each about 9 mm. 
in diameter and 15 mm. high; the fifth ten, and the sixth 
eleven; the seventh is incomplete. The mammillations of 
each row alternate in position with those of the preceding and 
succeeding series. Those of the rows above the fourth annu¬ 
lation become narrower gradually, those of the seventh being 
elliptical in outline, averaging 5.5 mm. in width by 9.5 mm. in 
length, with a hight varying between 1.5 and 2.0 mm. 
Sponge-wall exceeding thin, the thickness being less than 
0.5 mm. In the only example seen the minute details of its 
structure have been almost obliterated by replacement with 
iron pyrites. The outer surface, where best preserved, is finely 
reticulated, being traversed by lines and series of points 
ranged in very regular diagonally intersecting, tranverse and 
longitudinal directions. Measuring diagonally, 14 lines were 
counted in 5 mm. When a little worn the diagonal lines be¬ 
come fainter but the longitudinal ones proportionately more 
conspicuous. There is some evidence to show that this net¬ 
work was formed of overlapping hexactinellid spicules having 
the six rays spread in one plane. 
Formation and locality: Middle beds of the Cincinnati 
group. The type and only specimen seen was collected some 
years ago in the quarries on Roh’s hill, Cincinnati, 0., by Mr. 
Charles Schuchert, now of Albany, N. Y. It is now in the 
author’s cabinet. 
HETEROSPONGIA, n. gen. 
Sponges consisting of sublobate or irregularly divided, com¬ 
pressed branches. Entire surface exhibiting the mouths of 
branching and more or less tortuous canals, which begin near 
the center, where they are nearly vertical, and proceed toward all 
