ACROTHYRA — A NEW GENUS OF ETCHEMINIAN BRACHIOPODS. 
303 
ARTICLE IV. 
ACROTHYRA. 
A New Genus of Etcheminian Brachiopods. 
By G. F. Matthew, LL. D., F. R. S. C. 
/ 
(Read January 8, 1901 ; published January, 1901. 
In studying the earliest strata of the Eo-Palseozoic of the island of 
Cape Breton in Nova Scotia, Canada, the author has met with a form 
already described in the pages of this 
Bulletin as an Acrotreta,* but which 
from more perfect knowledge of the 
shape, habits and structure, he 
now thinks should be set off as a 
separate genus with the following 
characters : 
Quite small Brachipods having 
the ventral valve elongate-conical, 
with the apex either overhanging 
the cardinal line, or but little in 
front of it. Orifice nearly circular, 
often oblique. Interior with a 
long, narrow, or a quadrate visceral 
callus, extending forward from the 
foramen about a third of the length 
of the valve and widening as it goes. 
A distinct, usually high, cardinal 
area extends from the foramen to 
the cardinal line. 
Dorsal valve as in Acrotreta, 
The difference in the form of the 
Acrothyra proavia, mutprima- , yal distinguishes this 
1, Ventral valve — 2, Mould of the ° 
same — 3, Same in profile— 4, Dorsal genus from Acrotreta and is accom- 
valve-5, Mould of the same-6 . Same panie dby difference of habit, etc. 
in profile. All magnified ' T ° Upper r J 
Etcheminian Shale, C. Breton, N. S. In Acrotreta the visceral callus is 
* Acrotreta proavia, this Bulletin, vol. iv., p, 203. 
