IQI5] PALAEOZOIC FossILs FROM HUDSON Bay. 41 
short, there is evidence of a more rapid tapering than is shown by the 
other species. The septa, epitheca and tabule are all extremely deli- 
cate. Whether these structures were strengthened during the life of 
the organisms by deposits of stereoplasma, or whether the present con- 
dition of the specimens is due entirely to subsequent deposition of 
calcite, I cannot with certainty assert, but I am strongly inclined to 
the latter view. 
The decorticated exterior (Pl. I, Fig. 2) shows vertical furrows 
3-5 mm. apart at a diameter of 25 mm. In the second fragment, which 
evidently belongs to a larger specimen, these depressions are fully 4 mm 
apart. Between these major furrows, is another scarcely less pro- 
nounced. A third order of furrows, somewhat less distinct, occurs 
between those of the first and second orders. Delicate transverse 
growth lines are also to be seen. 
The major set of furrows corresponds in position with the primary 
septa, which in the larger specimen extend inwards 3 or 4 mm. At a 
diameter of 25 mm. about 22 primary septa occur. The secondary 
furrows probably represent the position of secondary septa, but only 
the slightest indication of these can be seen. The third order of furrows 
probably represents a third order of septa, but no evidence of their 
extension inwards is to be observed. 
The tabulze are complete, horizontal, and about 8 mm. apart. In 
the centre they are quite flat, but at the periphery they are sharply inflected 
downwards between the primary septa: this gives the line of junction 
between the tabulz and the epitheca a crenulated appearance. The 
secondary septa produce an extremely slight upward inflection of this 
downward fold but the tertiary septa, if present, have no effect on the 
crenulation. Viewed from above, a tabula shows ridges marking the 
position of the primary septa and extending inwards a distance of 7 mm. 
There can be no doubt that this form is close to the genus Amplexus: 
the downward inflection of the tabule and the continuation of the 
septa as ridges on the upper side of the tabule point strongly to that 
genus. On the other hand the general resemblance to Pycnostylus 
elegans is pronounced, especially in view of the fact that some crenu- 
lation of the margins of the tabule was observed in certain examples 
of that species (See page 40). If absolutely no crenulation of the 
tabular margins is permissible in Pycnostylus then the present form 
must be transferred to Amplexus. 
Locality—Limestone rapids, Severn river, District of Patricia, Ontario. 
Horizon—Silurian. 
No. 303 S. Royal Ontario Museum of Palaeontology. 
