94 ROYAL SOCIETY OF CANADA 
Acrotreta the visceral callus is concentrated around the foraminal pas- 
sage, and the shell appears to have been of sedentary habit, since the 
ventral valve in many cases is found fossil in such an attitude as to show 
that this valve stood in a vertical position in the mud of the sea bottom 
when the animal which inhabited it was living, the opening of the valve 
being uppermost. No such uniformity of attitude characterizes the 
dorsal valve. 
We find that the ventral valve in Acrothyra assumes quite a dif- 
ferent attitude. It lies in almost all cases on its side, and usually with 
the opening of the valve uppermost. Moreover, it is to be noted that 
on successive layers these valves lie with the umbo oriented in a fixed 
direction. From this it may be inferred that they give evidence herein 
of the action of a current, flowing in a definite direction and sweeping 
the valves in the direction towards which the current set. They may 
have swung in this direction by the pedicle while the animal was living ; 
or when swept away by the flowing water, have presented the point of 
least resistance to the current, as they sank to the bottom. In either 
case we must regard Acrothyra as living under different conditions from 
Acrotreta, which, as we have remarked, apparently had the apex of the 
ventral valve buried in the mud. 
It is in accordance with these conditions that we have in Acrothyra 
a visceral callus developed along the.median line of the ventral valve, 
as is the case in Lingula and other allied genera ; and Lingula, as is 
well known, had a long pedicle. 
This genus is peculiarly Etcheminian, there being two species and 
several varieties or mutations in the strata of this age. It seems likely 
Lingulella (?) inflata of the Protolenus Fauna belongs to Acrothyra ; 
if so, the genus ranges up into the Primordeal Cambrian. 
Conotreta, of Walcott an Ordovician (Trenton) genus, is a later 
development from the Acrotretoid phylum, differing in the form of 
the visceral callus, which is pointed in front, in place of expanding, as 
in Acrothyra. Analogy, however, would lead us to infer that this genus 
also was free-floating, and not sub sedentary, like many species of 
Acrotreta. 
This type of Brachiopod—Acrothyra—is one of the earliest known 
in the Paleozoic rocks of Canada, being found in shaly layers in the © 
midst of the eruptives which mark the advent of Paleozoic Time in 
Eastern North America.” 
Among the peculiarities notable in this genus are the elongate form 
of the ventral valve and the long callus on its interior. The form is 
more worm-like than other Brachiopods, and in this more like Hyolithes, 
but the callus in position and form is much like that of an elongated 

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