14 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



Esperia, and similar to Esperites haldonenses Carter. 1 Fossil forms have 

 also been figured by Hinde. 2 



Figure 10. Reniera 1 ? 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. 3 This is not an uncommon form in the flints. 



Figure 3G. Reniera 1 ? 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. 4 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. 



TETRACTINELLID^, 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. The 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 man}' 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-stelhite 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, 



i Ann. Mag. Nat. Mist., Ser. 4, 1871, Vol. XII. p. 131, Plate IX. Fig. 43. 



2 Phil. Trans. K, s., Part II., 1886, p. 437, Plate XL! Fig. 12. 



; ll,i,l., 1886, p 487, Plate XLI. Figs. I le 



4 Fossil Sponges in the Upper Chalk, p. 23, Plate I Fig. 17. 



