128 BRITISH PALAEOZOIC SPONGES. 



11. Dictyophyton Danbyi, M'Coy, sp. Plate II, figs. 4, 4 a, 4 5, 4 c. 



1852. Tetragonis Danbyi, WQoy. Brit. Pal. Foss., p. 62, pi. i », figs. 7, 8. 

 1854. — — Morris. Cat. Brit. Foss., p. 90. 



1872. — — Murchison. Siluria, 4th edit., p. 509. 



1873. — — Salter. Cat. Cambrian and Sil. Foss. Cambridge, 



p. 176. 



1880. — — F. Roemer. Letha;a pal., p. 304. 



1881. — — Whitfield. Bulletin Amer. Mus. Nat. Hist., No. 1, 



p. 14. 

 1883. — — F. Roemer. Zeitschr. d. deutsch. geol. Gesellsch., 



p. 707. 

 1883. Dictyophyton Danbyi, Hinde. Cat. Foss. Sponges, p. 131. 



Sponges sub-ovate or sub-conical in form, growing from an obtuse basal point, 

 without stem, root, or point of attachment, the base is flattened or convex, the 

 greatest width in some specimens is just above the base, in others about half the 

 height of the Sponge, from this it gradually tapers to the summit, which appears 

 to have been open. The specimens vary between 23 and 30 mm. in height, and 

 from 14 to 17 mm. in width. 



The Sponge- wall appears to have been smooth and even ; the larger areas of the 

 rectangular meshwork are marked out by more prominent, vertical, and transverse 

 raised lines, and vary from 1"5 to 3 mm. in length, and these are subdivided by 

 finer lines into smaller squares, the sides of which are about *75 mm. in length. In 

 some cases the stronger lines forming the larger squares are nearly parallel from 

 the base to the summit, whilst in others they converge to each other towards the 



No spicular structure whatever has been preserved in any of the specimens yet 

 discovered, which are merely casts in a matrix of micaceous sandstone. No struc- 

 ture can be detected in the interior of the specimens. 



Mr. Salter, according to M'Coy's statement, referred this species to Receptacu- 

 lites ; by M'Coy himself it was placed in the genus Tetragonis, Eichwald, and 

 apparently regarded as belonging to the Echinodermata ; and in Morris's Catalogue 

 it is also placed in this group. Ferd. Roemer likewise includes this species under 

 Tetragonis, and calls attention to the resemblance between the surface characters 

 of another form of this genus and Dictyophyton. Subsequently I placed the species 

 in Dictyophyton, as its structure, so far as a comparison is possible from merely the 

 casts of the organism, agrees closely with that of D. tuberosum, Conrad, the type 

 of the genus. It is now known that the genus Tetragonis, Eichwald, is merely a 

 synonym of Ischadites, Murch., and its characters markedly differ from those of 

 Dictyophyton. 



