MERRILL: FOSSIL SPONGE SPICULES. 13 



Figure 6. Imperfect. This spicule has been replaced by amorphous 

 silica of au opalescent hue, the dark portion of which represents the 

 replacement of the axial canal enlarged. It is covered with bulbous 

 projections or blunt spines, which are evenly arranged toward the apex, 

 but become more irregular toward the extremity. It has the appear- 

 ance of being thiu and flat rather than cylindrical. It is 0.0843 mm. 

 long, by an average width of 0.0844 mm. It has not been found 

 figured. 



Figure 7. This spicule is imperfect and irregular in outline, the 

 irregularity seemingly composed of folds in the outer coveriug of the 

 spicule. The outline seems to be in peroxide of iron, or some kind of 

 black organic matter, most likely the latter, since it has not the beaded 

 form common to the ore replacement. The interior is entirely of 

 amorphous silica, with a trace of an axial canal. A cross section of this 

 shows a thin black ring around a siliceous body. This figure is 0.52 mm. 

 in length by 0.08 mm. in width. This species is the most abundant of 

 the sponge spicules found in the flint, and the figure given represents its 

 most characteristic form. The summit of one has not been found, and 

 only occasionally is the apex found complete, while fragments and cross 

 sections are abundant. It was found in all the nodules examined, and 

 one was made up almost entirely of it. In the nodules above referred 

 to there are found what appeared to be irregular black tracings of the 

 outside layer of this spicule, curiously winding around in the flint and giv- 

 ing it a dark ringed appearance. This outside layer is sometimes thicker 

 than others, but is always distinct, and surrounds the spicule entire 

 unless broken mechanically. I have not found this spicule described or 

 figured. 



Figure 8. A fragment of a cylindrical spicule covered with very short 

 bulbous projections. The specimen is composed of a thin wall of col- 

 loidal silica, while the inside is filled with whitish amorphous silica, 

 no axial canal visible. Size of specimen : length, 0.266 mm. ; width, 

 0.106 mm. Of this I found but one specimen. One somewhat similar 

 is figured by Dr. Hinde. 1 



Figure 9. Esperites 1 sp. Almost perfect, but the ends not fully 

 shown. A bihamate spicule. Length, 0.266 mm., width, 0.026 mm. 

 Others found measure 0.386 mm. in length by 0.026 in width. Others 

 less typical in size show the peculiar bihamate ends better than the one 

 figured. This is a very common form in the nodules, nnd is found in 

 nearly every slide. It is probably some species of the recent family 



1 Fossil Sponges of Upper Chalk, Plate I. 



