U7 



adheres inextricably to the matrix, as shown in the woodcut. We must 

 therefore conclude that this surface was originally concave, or else we 

 must suppose that the basal concavity was caused by an alteration of its 

 original form, previous to fossilization, a view which is not borne out by 

 the regular contour of the specimen. 



A transverse section half way up through the fragment gives the 

 appearance represented between A and C on figure 1 of Plate 16. This 

 figure, considered in connection with the woodcut, proves that the skele- 

 ton fibres, in each of the radial rays, are pinnately arranged on both 

 sides of a vertical median plane, and that these fibres diverge upward 

 and downward as well as to the right and left. The distance between 

 the axes of the fibres would measure from 0'35 to 0-50 mm. Of an 

 integument layer I could find no traces. 



Although the skeleton has undergone a secondary silicification, and has 

 therefore for the most part become obliterated, there is no doubt that, in 

 structure and dimensions, it corresponds with that of Atdocopium or the 

 American Z.ittelella. 



Figures 2 and 3 of plate 16 are attempts at a restoration of this sponge, 

 the diagrams being one-third the natural size. Figure 2 shews a side 

 view, and figure 3 a basal view of the organism, as it is supposed to 

 have been when entire. The sponge had the form of a cog-wheel, with a 

 diameter of at least 150 millimetres and a height of 75 mm., from whose 

 conical hollow axis (about 40-50 mm. in diameter) eight radial rays pro- 

 ceed, which are 15-20 mm. thick and 50 mm. long at the midheight. 

 From the mouth of the Paragaster, surface furrows radiate downward 

 over the convex summit and upper surface of the rays. The naked 

 basal surface is concave. In each ray the skeleton fibres are symmetri- 

 cally arranged to a radial vertical median plane. 



Trichospongia hysteix. (N. Sp.) 



Plate 17, fig. 3. 



The foregoing name is proposed provisionally for a single specimen of a 

 sponge, in which the main portion of the body skeleton is represented by 

 a light brown or pale ferruginous impression or stain on the flat surface 

 of a piece of limestone, with its margin outlined by a darker tint. This 

 impression is rather narrowly elongated, about five times as long as high, 

 with the base nearly straight but slightly convex in the middle, the 

 summit still straighter, and the two ends narrowly rounded. Lying 

 across it are numerous, exceedingly narrow, straight and apparently 

 simple spicules, which project beyond the summit and ends to a maxi- 

 mum distance of eight millimetres. Exclusive of the projecting spicules, 



24 



