Westphalia, (Zittel: iiber Coelop. Taf. VI, figs. 16—29) 
and in the Eocene sand of Brussels (Rutot: op. cit. Pl. IU, 
fig. 9). 
Quadrifid Spicules of Pachastrella. 
Pachastrella, sp. 
(late Mee hess §24e 25) 
Simple quadrifid spicules in which three elongated arms 
radiate at equal angles from a centre and form the outline 
of a more or less elevated three-sided pyramid, from the apex 
of which another arm generally shorter than the other three, 
extends upwards. There are two very distinct forms of these 
simple quadrifid spicules. In the larger (fig. 24) the three 
arms form a very low pyramid; in some examples they are 
nearly in the same plane; and the fourth arm, much shorter 
than the other three, is nearly at right angles to them. The 
other three arms are nearly equal, straight and pointed, and 
in no instance which I have noticed are they bifurcated at 
the extremities. Canals are shown in some examples, much 
wider than those in similar spicules of recent sponges. These 
spicules are abundant and very uniform in size. The average 
length of the arm of a fair sized spicule is 1,035 mm. and 
its thickness near the centre is 0,09 mm. The vertical arm 
has a length of 0,2 mm. 
In the smaller form of quadrifid spicule (fig. 25) the four 
arms are nearly equal in length and they are disposed so as 
to form a more elevated pyramid. The average length of 
each arm is 0,45 mm. and the thickness near the centre 
0,045 mm. These spicules are also very abundant. 
From comparisons which I have made with specimens of 
Lachastrella amygdalordes, Carter, and P. geodioides , Carter 
(An. Mag. Nat. Hist., S. 4, Vol. 18, p. 406, Pl. XIV, figs. 22 
<<y5 
23) from the Atlantic, I find that there is a striking resem- 
