CAMBRO SILURIAN MICRO-PALAEONTOLOGY. 25 



and differs from the latter only in having thicker and more wavy tubo- 

 walls, which are in somewhat closer proximity. No tabulae have been 

 seen in any of the Canadian specimens. As to their occurrence in the 

 Scotch species Mr. K. Etheridge, jun., in a letter lately received by the 

 author writes: — ''With regard to the presence of tabula) I must confess 

 myself in doubt. Some specimens undoubtedly do not possess them, a 

 fact which has already been commented on by Dr. Nicholson and myself, 

 (Girvan Report, facie. 1, p. 32), but again in some sections I have seen 

 horizontal divisions of the tubes, which I could refer to nothing else." 



Taking into consideration the excessive minuteness of the corallites, 

 and the sinuosity of their walls in Tetradlum Peachiif and its variety 

 Canadensis, and the doubtful existence of tabula) in both, it would seem 

 necessary to remove these forms from the genus Tetradlum, The pro- 

 priety of this course has perhaps occurred to the authors of the species. 



Locality and Formation. — Abundant throughout the Trenton formation 

 of the Province of Quebec, at the following localities: Hull, Jolietto, 

 Montmorency and Murray Bay. 



CoUcrtors: — Piincipal Dawson, T. C. Weston, II. M. Ami, A. 11. Foord. 



Tetradium Huronense, Billings, Sp. 

 Plate VII.; figs. 1,-Ie. 



^tenopora Iluronensis^ Billings, Pal. Foss., Vol. I., p. 185, 1801-18C5. 



A microscopical examination having been made to ascertain the aflS^ni- 

 tics of the Stenopora Iluronensis, of Billings, it was found to belong to the 

 genus Tetradium, The following is the amended description : — 



Corallum very largo, massive, rounded, growing in thin concentric 

 lamina), of about 1 to 2 mm. in thickness. Some specimens attain a 

 diameter of about 30 centimetres, and an average thickness of about 7 

 centimetres. Corallites extremely long, from 6 to 12 centimetres in 

 length. The surface is covered with prominent, rounded, or conical 

 elevations, and these arc seen on weathered, or polished sections to have 

 covered the surface of each successive lamina of which the corallum was 

 built up ; this lamination gives to the fossil somewhat the appearance of a 

 Stromatopora, as observed by Mr. Billings. The elevations are from four 

 to six centimetres apart, measured from their summits ; in height they 

 are about 3 mm. The entire surface of the corallum, including the conical 

 elevations, is covered with close-set, rounded granules, of which about 

 three fill the space of I mm.; they diverge from the summit of the eleva- 

 tions in a stellate manner. 

 4 



