428 THE CANADIAN NATURALIST. [Dec. 



so. Colonies are occasionally found with the cells distant about 

 half their diameter. 



The species to which this is most nearly related is H. tubulata 

 (Lonsdale), common in the Wenlock limestone. That species how- 

 ever, as described by McCoy, Edwards and Haime and others, has the 

 cells in general somewhat smaller and the apertures not so strongly 

 serrated. 



The crenulations on the margins of the cells are only visible when 

 the surface is not at all abraded. The least wearing removes them, 

 and the apertures are then simply circular or sub-polygonal. 



This species has been found at Wreck Point, Anticosti ; in the 

 Hudson River formation. Also at White Cliff, Junction Cliff. 

 Walls Cove, South Point and other localities, on the same island, 

 in Divisions 1, 2 and 3; Anticosti group; Middle Silurian. J* 

 Richardson and T. C. Weston. 



H. exiguus. — Cells about half a line in diameter and somewhat 

 more than their own width distant from each other, with thin 

 elevated margins, apparently not crenulated. Septa not visible in 

 the only specimen collected. Tabulae numerous, four to six in 

 one line. Coenenchyma minutely vesicular. 



As the specimen is somewhat worn, it is possible that the mar- 

 gins of the cells when perfect maybe crenulated. The ccenenchyma 

 appears to be vesicular, but more specimens are required to decide 

 this point. 



This species, on account of the small size of the cells and their 

 greater proportional distance from each other, seems to be distinct 

 from all the others. 



H. sparsus. — Cells varying from half a line to one line in 

 diameter, distant from one to three lines from each other. Radi- 

 ating septa much developed, sometimes meeting in the centre. 

 The coenenchyma varies in structure, being in some places entirely 

 vesicular, and elsewhere composed of vertical series of square cells 

 as in H. megastoma. These variations are seen in the same 

 specimen. Chicotte River, Anticosti ; Division 4 ; Anticosti 

 group ; Middle Silurian. J. Richardson. 



H. tenuis. — Cells, in general, a little less than half a line in 

 diameter, and half their own width distant, The walls are exces- 

 sively thin and rarely distinguishable, not forming a distinct ring 

 as in the others above described. Coenenchyma, as seen upon the 

 surface, composed of minute polygonal cells. This species may. 



