SS Xs) 
Horstead flint, and they are in a much more perfect state of 
preservation. 
In describing these Horstead spicules, I propose to begin 
first with the simple uniaxial forms and then pass on to the 
quadriaxial spicules and the more complicated lithistid and 
hexactinellid forms; following the systematic arrangement which 
is given by Professor Zittel in his «Beitrage zur Systematik der 
Fossilen Spongien». 
Monactinellide, Zittel. 
To this order belong those sponges whose skeleton con- 
sist only of those spicules which possess a single unbranched 
interior canal. But as simple monaxial spicules are also 
common to other orders of sponges as well, the question of 
determining the proper relationship of these spicules, when 
detached, as in the specimens under consideration, is some- 
what involved. As the only method available, I have com- 
pared the simple uniaxial spicules in this deposit with those 
which are present in recent and fossil sponges of the order, 
as well as with the uniaxial spicules which are found in con- 
nection with the distinctive spicules of Geodia and other genera, 
and I have come to the conclusion that the greater number 
of the uniaxial spicules in this deposit more probably belong 
to Geodia and thus formed part of the Skeleton Spicules of 
Tetractinellid sponges, under which I shall include them. 
Those which appear to have belonged to Monactinellid sponges 
are not very numerous. 
Acuate Spicules. 
(Plate I, figs. 1o—15.) 
Simple acuate spicules, somewhat resembling pins, but 
with less prominent heads, curved, thickest at one extremity 
and gradually tapering to the other, which in some instances 
is obtusely pointed. Originally smooth, though now with 
