14 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
Esperia, and similar to Zsperites haldonenses Carter." Fossil forms have 
also been figured by Hinde.? 
Figure 10. Reniera? sp. This spicule is replaced on the outside by 
chalcedonic silica, and part of the inside by peroxide of iron. Length, 
0.26 mm., width, 0.013 mm. It may be referred to some form of 
Reniera similar to but smaller than Reniera Zittelli, Pocta, figured by 
Hinde? This is not an uncommon form in the flints. 
Figure 36. Reniera? sp. Outline perfect. Has typical form of Reni- 
era. Curved, cylindrical, and rounded similarly at the ends. Length 
0.48 mm., width 0.106 mm. It is replaced by amorphous silica. This 
is a common form here and also in Europe. Figured by Hinde.* This 
specimen was found on the outer margin of the nodule embedded in the 
silicified chalk. It is rather larger than the average of its kind. 
TETRACTINELLIDAH, MARSHALL. 
This order contains sponges with skeletal spicules of the pyramidal 
type. In addition to those which are the principal or zone spicules, 
there are dermal or flesh spicules which are characteristic of the living 
forms, but which are rarely ever found fossil. These last are most abun- 
dant in the Texas flint nodules. Of the first, several were found generally 
imperfect, the one shown in Figure 32 being the smallest in size, but 
most perfect in form and condition of preservation. Тһе spicules of the 
flesh and dermal layers are of various forms and have received various 
names, ‘They were first thought by Bowerbank to be the reproductive 
system and were called siliceous balls; they were afterwards called glob- 
ular crystalloids, spino-globates, and globo-stellates by Carter. They 
are all more or less circular in outline, and many are globular, and 
nearly all are covered with spines. Four varieties were found in the 
slides examined ; the thin, smooth, circular transparent disk ; the spino- 
globate, Figure 30, flat, with spines apparently around the periphery 
only; the globo-stellate with the spherical centre and short simple spines ; 
and the globo-stellate with spherical centre and long spines divided into 
barbs at the end. 
The last two divisions named are peculiar from the fact that the 
spines are hollow tubes branching from the hollow centre, thus allowing, 
1 Ann. Mag. Nat. Hist., Ser. 4, 1871, Vol. XII. p. 131, Plate IX. Fig. 43. 
2 Phil. Trans. В. S., Part IL, 1885, p. 437, Plate XLI. Fig. 12. 
в Ibid., 1885, p. 437, Plate XLI. Figs. 4-4e. 
^ Fossil Sponges in the Upper Chalk, p. 22, Plate I. Fig. 17. 
