380 
HULLETIX OF THE NATURAL HISTORY SOCIETY. 
brian trilobite so far described ; but the Hyolithes may be a form 
of //. americanus of Billings. 
The writer has suggested the possibility that from the composition 
of the Hastings Cove Paradoxides fauna, the genus Olenellus, sens, 
strict., might occur above Paradoxides. This now seems the less 
probable from the occurrence in Cape Breton of the latter genus as 
high up as the middle of the Johannian division, where Olenus would 
naturally be looked for. It would seem that Olenellus must occur 
lower down than the Johannian division. 
New Species of the Etcheminian or Basal Cambrian. 
1 . — Development of the genera Acrothyra^ Acrotreta and Acrothele. 
The value of small species of fossils in determining geological hori- 
zons is well shown in Tullberg’s monograph on the Agnosti, of which 
genus certain types are peculiar to special horizons of the Cambrian 
and of the Ordovician. A small fragment of rock only has been found 
sufficient, when containing certain Agnosti, to determine the age 
of a group of strata. 
I hope it may hereafter be possible to use the three genera above 
mentioned in a similar way for determining the age of parts of the 
Etcheminian and the higher Cambrian, where these genera occur. It 
is as a contribution to this object that the writer presents here de- 
scriptions of such species and varieties as have been recognized in the 
Canadian Cambrian rocks. * 
It will be seen that so far as our knowledge goes, the first two gen- 
era are among the oldest that have been recognized in the Cambrian 
rocks of Flastern Canada, since they are found among the volcanics 
that lie at the base of the Paheozoic terranes, as well as higher up in 
the Cambrian ; and they were distinct from each other, even at that 
early time. 
The following table shows the distribution of these early forms of 
Brachiopods in the basal Cambrian rocks and their relative abundance 
at Dugald Brook at the several horizons at which they occur : 
