58 SILICEOUS SPONGES. 



mesh is for the most part dissolved away, and only empty moulds remain ; in a few 

 instances, however, the spicules remain, and are now of a reddish material. The 

 canals have been filled with cherty silica, and the minute projecting rods connecting 

 adjoining canals have been produced by the silica filling in the minute spaces between 

 the spicular mesh. This appearance Eoemer mistook for the infilling of connecting 

 tubes in the wall of a coral. The condition of these sponges from Tennessee is 

 precisely similar to that of specimens of Astylosjjonrjia ; and no doubt can be enter- 

 tained that, like this last-named genus, they were originally siliceous. The examples 

 from New Brunswick, however, have had their original skeleton replaced by calcite ; 

 and this fact led Prof. Duncan to believe that they were originally calcareous, so that 

 " there must have been a former mimetic and calcareous group of Spongida." The 

 character of the spicules cannot be so clearly seen in the calcite specimens ; and after 

 a close examination of the forms from Tennessee and New Brunswick, I believe that 

 the spicular elements resemble those of the Anomocladine family rather than of the 

 Tetracladina. 



The Tennessee examples appear to have been completely spherical, those from 

 New Brunswick are oblate spheroidal in form ; the internal structure and dimensions 

 of the canals appear to be the same in the sjionges from both localities. 



Distribution. Silurian (Lower Helderberg Group): near Dalhousie, New Brunswick ; 

 Perry county, Tennessee [Pearson's coll.). I have also seen specimens of the same 

 species from the Lower Helderberg group at Schoharie, New York. 



Family TETMACLADINA, Zittel. 

 Genus AULOCOPIUM, Oswald, 1846. 



AuLOCOPiUM CTLiNDBACEUM, Fenl. Roemer. 



1861. Aulocopium cylindraceum, Roemer, Fossile Fauna von Sade^itz, p. 9, t. 3. f. 2a, 2b. 

 1878. Aulocopium cylindraceum, Zittel, Studien, II Ab. p. 73. 



Distribution. Silurian : Gotland. 



Genus PHYMATELLA, Zittel, 1878. 



Phtmatella intumescens, Rcemer, sp. 



1864. Eudea intumescens, F. A. Roemer, Palaeont. Bd. 13, p. 26, t. 11. f. 1. 

 1878. ScypMa intumescens, Quenst. Petref. Bd. 5, p. 392, t. 133. f. 23-26. 

 1878. Phymatella intumescens, Zitt. Studien, II Ab. p. 74. 



There is but a single imperfect example of this species in the Museum collection, 

 which is cylindrical in form, tapering near the base, with irregular hollows in its 



