curved, of which three are disposed nearly in a plane or 
forming a very depressed pyramid. One arm of these three 
is frequently longer than the others, slightly curved, and at 
the extremity bifurcates into two small irregular rays (fig. 32, 
33). The arm at the apex of the pyramid is short and obtusely 
blunted and in some instances is continued beyond the apex 
of the pyramid, so that a five-armed spicule is the result, 
(figs. 28, 34), As in other respects these five-armed spicules 
correspond closely with the four-armed, Iam disposed to consider 
them as mere variations and not as indicating a different species. 
The length of the arms of these spicules varies between 0,495 mm. 
and 1,125 mm. with an average thickness of 0,14 mm. The 
examples of these quadrifid spicules are but rarely met with. 
These spicules correspond so closely with those of 
Pachastrella primoeva, Zittel, from the Upper Chalk of Ahlten 
in Hanover, that, so far as can be judged from the zone 
spicules, they may have belonged to the same species. In 
the Ahlten sponge, the larger spicules are also accompanied 
by great numbers of the smaller simple quadrifid spicules 
similar to those of my fig. 25, and these smaller forms both 
in the fossil and recent sponges seem common to different 
species of Pachastrella. I have also seen a specimen of Pachastrella 
from the Flamboro’ Chalk, given by Mr. Carter to Professor 
Zittel, in which the furcation of the skeleton spicule is carried 
to a greater extent than in the Ahlten and Horstead examples, 
and the spicule is also Jess robust. In the furcation of the 
extremities of the spicule, the Chalk examples correspond 
closely with the skeleton spicules of VPachastrella abyss?, 
O. Schmidt, and also with P. zutertexta, Carter. (An. Mag. 
Nat. H. S. 4. Vol. 18. p. 409 Pl. XV. fig. 41) dredged from 
the Atlantic near Cape St. Vincent at a depth of 374 
fathoms. Examples of the five-armed spicules also occur in 
P. mtertexta and in P. parasitica, Carter (An. Mag. Nat. Hist. 
5214. iNVol. 182 p, 410 Ph. XV) fig: 50,) 
