12 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



Annals and Magazine of Natural History. 1 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. 



MONACTINELLID^E, 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 in the fossil state. The spicules referred to it 

 are frequently so much like the zone spicules of other groups that it u 

 extremely hard to separate them, and to decide whether the spicule in 

 question belongs to Monactinellidae or some other group which ha? 

 spicules of a single shaft. The acuate spicules that I have referred tc 

 this group have been so referred mainly on their similarity in size and 

 shape to those figured by Dr. Hinde. 2 



Figures 1 and 2. Axinella? Imperfect. Replaced by chalcedonic 

 silica. Canal well shown, polarizes differently from the body, showing a 

 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 dispersal These forms are not rare in the 

 nodules, but are never found perfect. 



Figures 3 and i. Renieral Conical spicules even in outline, with 

 axial canals well shown, liases broad, tapering gradually to apex. 

 Replacement is by crystalline silica. Size of Figure 3 : length, 0.373 

 mm.; width, 0.093 mm. These are probably some form of Reniera. 

 Similar figures, lint larger, arc found in the Upper Chalk, 4 and also in 

 the Upper and Lower Greensnnd. 6 



Figure 5. An acuate spicule in amorphous silica surrounded by a 

 thin layer of chalcedonic silica. Length, 0.64 mm.; width, 0.08 nun. 

 Similar spicules have been figured by Hinde. 6 



1 Ser. 4, Vol. XX.. nnd Ser. 6, Vols. IT. and V. 



— il Sponges of the Upper Chalk and Sponge Ilemains of the Upper and 

 Lower Greensand, Phil. Trans. Royal Soc, 1885, l't. II. 



8 Phil. Trans. Royal Soc, 1886, Part II., p. 137, Plate XLI. Figs. 6-4 

 4 Fossil Sponge Spicules, p. '-':!, Plate I. Figs. 19 anil Lit. 

 » I'hil. Trans. R. S, l't. II., 1885, p. •-'•-', Plate XLI. Kig. la. 

 ! iil £ Upp< r i hulk. pp. -jo, 21, Plate I Fig. 1 1 



