94 CONTRIBUTIONS TO CANADIAN PALAEONTOLOGY. 



Specimens of Tetradium have been collected from the Hudson River 

 formation at Cape Smyth, Lake Huron, and at Streetsville, Ont., that 

 have corallites varying in width from Jrd to J of a line. The tabulae in 

 these specimens are as a rule preserved ; they are flat and from four to 

 ten occur in a space of 1 line. The septa show the same variation in 

 development as is found in those of the Birdseye and Black River speci- 

 mens, and the corallites also vary in size to some extent in individual 

 specimens. 



A specimen of Tetradium collected by Prof. J. H. Panton from rocks 

 of Galena-Trenton age at East Selkirk,* Manitoba, has corallites of rather 

 unequal size, varying in width from not quite Jth to ^ of a line. The 

 tabulse are delicate, flat and placed about ^th of a line apart. The septa 

 extend only a very short distance from the walls of the corallites toward 

 the centre. 



If in T. Jibratum the corallites vary in width from ^th to fths of a line, 

 and in T. minus from ^th to ^rd of a line, and that this constitutes the 

 sole difference between the two species, then it would be difficult to tell to 

 which of these species many Canadian specimens from the above men- 

 tioned horizons belong, as the majority of those examined have corallites 

 that range in width from ^th to J of a line. 



The writer has not observed any differences in structure in Canadian 

 specimens of this coral that are, in his opinion, sufficient to warrant a 

 specific or even a varietal subdivision ; they are therefore here referred to 

 under the name T. Jibratum. 



In his " Contributions to the Micro-pal seontology of the Cambro-Silur- 

 ian rocks of Canada " Mr. A. H. Foord has described under the name 

 T. Huronense two distinct forms, one the Stenopora Huronensis of 

 Billings, since found to be a Labechia, the other T. jibratum, Safford. 

 The specimens referred to and figured by Foord are in the museum of the 

 Geological Survey, and are from the Hudson River formation at Cape 

 Smyth, Lake Huron. The specimen represented in plate VII., fig. 1, of 

 Mr. Foord's paper, is a mass of T. fibratum coated* to a thickness of from 

 about 11 to 2 lines by Labechia. Huronensis, Bill. Figure la is a 

 representation of a portion of a mass of Labechia Huronensis and figs, lb, 

 lc, Id, le illustrate the structure of T. fibratum (poorly preserved) as 

 seen in horizontal and longitudinal sections, taken from the specimen 

 shown in fig. 1. 



* This specimen was received as a donation from the Peter Redpath Museum through 

 Sir J. William Dawson, and had previously been recognized as Tetradium fibratum by- 

 Prof. Panton and Mr. Whiteaves. 



