18 
to become established. Other shells in the fauna appear to be free of 
these parasitic creatures. The largest specimen of S , striatula has a length 
of 33 and width of 36 mm. 
Relations of the Peace Point and Fort Simpson Shale Fauna 
The position in the New York section of the Ithaca fauna with which 
this Peace Point fauna is correlated was long misunderstood. James 
Hall first correlated it with the Chemung, where it remained until H. S. 
Williams showed by the study of a series of east-west sections across New 
York state that the Ithaca fauna was the eastern or inshore equivalent 
of the Portage fauna of western New York. The writer considers the 
Peace Point fauna to have precisely the same relationship to the Simpson 
shale 1 fauna of Mackenzie valley that the Ithaca fauna bears to the New 
York Portage. The occurrence of this fauna in the easternmost of the 
Palaeozoic exposures of the Peace River section and the location of all the 
known sections of the Simpson shale far to the westward of the eastern 
margin of Devonian sediments are in harmony with the inference that the 
Simpson shale and Peace Point faunas were contemporaneous western and 
eastern faunas of the same early Upper Devonian sea in which the temper- 
ature differed along more or less parallel north and south belts or in 
discontinuous areas near the eastern Devonian sea border. A comparable 
example of discontinuous distribution on the Atlantic coast of Canada 
is the Venus mercenaria fauna of Northumberland strait, which comprises 
an assemblage of molluscs fundamentally different from that found else- 
where in the gulf of St. Lawrence. The Northumberland Strait colony, 
which includes such southern species as Ostrea virginica and Venus mercen- 
aria, is separated from the northeastern border of the New England zone 
of the Acadian fauna by the deep basin of the bay of Fundy and the 
Atlantic coast waters of northern Nova Scotia. The reason for this 
isolation becomes apparent on examination of a bathymetric chart of 
the waters of the Maritime Provinces. The whole of Prince Edward 
Island and Northumberland strait lie inside the 20-fathom line, and much 
of the broad strait has a depth of 10 fathoms or less. On the southeastern 
coast of Nova Scotia, however, the 20-fathomline approaches in many places 
to within one-half mile of the coast, and there is everywhere a narrow 
zone of shoal water inside the 100-fathom zone which renders it colder 
than the broad, shallow, warm waters of Northumberland strait. It 
illustrates well the fact that a zone of shallow water (if sufficiently close 
to and unprotected from deep waters) may serve as a faunal barrier as 
effectively as a land barrier. 
The Peace Point Devonian fauna is believed to be related to the 
Simpson shale fauna in the same general way that the Northumberland 
Strait fauna is related to that of the adjacent parts of the gulf of St. 
Lawrence. The Peace Point fauna is considered to be the eastern or 
inshore fauna of the two and to have extended an unknown distance toward 
or eastward of the present western margin of the Precambrian shield in the 
region of Slave River valley. 
‘ Kindle, E, M.: ‘‘The Discovery of a Portage Fauna in the Mackenzie River Valley”; Geol. Stxrv., Canada, 
Mus. Bull. 29, pp. 1-8, Pis. I, II (1916). 
