12 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Annals and Magazine of Natural History." References to other works 
are cited at the places where quotations occur, in order that investiga- 
tion of authorities may be handier for those who desire to follow the 
line of thought. 
MONACTINELLIDA, ZITTEL. 
To this group Zittel refers all sponges the framework of which consists 
of simple uniaxial siliceous spicules. It is regarded by him as a small 
and unimportant group iu the fossil state. Тһе spicules referred to it 
are freguently so much like the zone spicules of other groups that it is 
extremely hard to separate them, and to decide whether the spicule in 
question belongs to Monactinellidee or some other group which has 
spicules of a single shaft. The acuate spicules that I have referred to 
this group have been so referred mainly on their similarity in size and 
shape to those figured by Dr. Hinde.? 
Figures 1 and 2. Axinella? Imperfect. Replaced by chalcedonic 
silica. Canal well shown, polarizes differently from the body, showing : 
separate crystallization. Summits rounded. Body slightly curved, but 
tapering toward the point. Size of Figure 1 : length, 0.733 mm. ; width, 
0.08 mm. Size of Figure 2: length, 1.673 mm.; width, 0.133 mm. 
These spicules are perhaps some form of Axinella, Dr, Hinde has 
called a similar one Axinella dispersa.” These forms are not rare in the 
nodules, but are never found perfect. 
Figures 3 and 4. Reniera? Conical spicules even in outline, with 
axial canals well shown. Bases broad, tapering gradually to apex. 
voplacement is by crystalline silica. Size of Figure 3: length, 0.573 
mm.; width, 0.093 mm. These are probably some form of Reniera. 
Similar figures, but larger, are found in the Upper Chalk,* and also in 
the Upper and Lower Greensand.’ 
Figure 5. An acuate spicule in amorphous silica surrounded by a 
thin layer of chalcedonic silica. Length, 0.64 mm. ; width, 0.08 mm. 
Similar spicules have been figured by Hinde.® 
1 Ser. 4, Vol. XX., and Ser. 5, Vols. II. and V. 
2 Fossil Sponges of the Upper Chalk and Sponge Remains of the Upper and 
Lower Greensand, Phil. Trans. Royal Soc., 1885, Pt. IT. 
3 Phil. Trans. Royal Soc., 1885, Part IL, p. 497, Plate XLI. Figs. 6-бе. 
^ Fossil Sponge Spicules, p. 23, Plate I. Figs. 19 and 20. 
5 Phil, Trans. К. 8., Pt. II, 1886, p. 22, Plate XLI. Fig. la, 
6 Fossil Sponges of Upper Chalk, pp. 20, 21, Plate I. Fig. 14. 
