MERRILL: FOSSIL SPONGE SPICULES. 19 



figured here. It is very small, and the doubt cast by its size, together 

 with its incomplete form, led me to discard it after drawing it. It is 

 similar in form to one figured by Hinde. 1 Traces also similar to one 

 in the Annals and Magazine of Natural History 2 are common in the 

 slides. There is but little doubt, therefore, that Lithistid sponges were 

 present in the flint forming ocean bottom, although through the acci- 

 dents of nodule formation they have all been destroyed. The following 

 spicule I have provisionally placed with the Lithistids. 



Figure 23. Irregular in outline. Transparent, yellowish, with smooth 

 surface. Has the appearance of colloidal silica slightly colored. 

 Length, 0.173 mm.; width, 0.09 mm. Similar spicules are figured by 

 Dr. Hinde. 3 



HEXACTINELLID^ll, Oscar Schmidt. 



In this order the siliceous skeleton consists of elements founded 

 almost without exception upon three axes crossing each other at right 

 angles. This group is poorly represented in the Texas flint nodules, 

 though Figures 33 and 34 are common. 



Figure 33. Spicule imperfect. Form quadradiate with arms extend- 

 ing almost the same size throughout in a, and tapering slightly in b. 

 Axial canal faintly shown in b, and lower arm turned slightly upward, 

 making an angle with the other. Length of arms varies from 0.26G mm. 

 in a to 0.466 mm. in b. They may have been considerably longer, 

 however, when perfect. Similar spicules are figured by Hinde from 

 Greensand of Halsmere and Blackdown, 4 and given the name Stauracti- 

 nella. Professor Zittel figures one also nearer the size of one in the 

 Texas fliut. s It is perhaps a little smaller, but more nearly perfect. 



Figure 34. Part of framework of Stauractinella % The four arms are 

 slender, and of uniform size throughout the whole length ; one arm is 

 represented by a small projection from the joint, and another arm is 

 absent ] The replacement is by peroxide of iron, which appears in bead- 

 like balls mixed with amorphous silica. Length of arms, 0.186 mm. 

 to 0.266 mm. This is similar to one mentioned by Dr. Hinde. 6 • 



Figure 35. Mesh spicule % The size of this spicule, as well as its 



1 Fossil Sponges in Upper Chalk, p. 5, Fig. 4. 



2 Ser. 5, 1878, Vol. II., Plate VII. Fig. 7. 



3 Fossil Sponges in Upper Chalk. 



4 Phil. Trans. R. S., Part II., 1885, p. 446, PL LXVI. Fig. 10a. 



6 Abh. d. II. cl. d. K. Ak. d. Wiss., XII., Bd. III., Abth., Taf. V. Fig. 53. 

 Phil. Trans. R. S-, Part II., 1885, p. 440, PI. LXVI. Figs. 10 and 10a. 



