SECTION IV., 1901 [ 93 ] Trans. R. 8. C. 
VIII.—Acrothyra and Hyolithes—a comparison. 
By G. F. MATTHEW, D.Sc. 
(Read May 23, 1901.) 
' 
Among the Brachiopods most common in the oldest Paleozoic 
rocks in Eastern Canada are certain minute shells of a conical shape 
resembling in form some of the shorter species of Hyolithes. These 
heretofore have not been separated from Acrotreta ; their distinctness, 
however, will be seen by the following description. 
“Article IV. Acrothyra. A New Genus of Etcheminian Brachio- 
pods. By G. F. Matthew, LL.D., F.R.S.C: 
“In studying the earliest strata of 1 2 
the Eo-Palæozoic 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 fol- 

lowing characters: 
Quite small Brachiopods 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 vis- 
ceral 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 Acrothyra proavia, mut. prima— 
1, Ventral valve—2, Mould of the 
D oa ; same—3, Same in profile—4, Dorsal 
orsal valve :s in Acrotreta. valve—5, Mould of the same—6, Same 
The difference in the form of the in profile. All magnified 1’ Upper 
ventral valve distinguishes this genus Etcheminian Shale, C. Breton, N.S. 
from Acrotreta and is accompanied by difference of habit, ete. In 


cardinal line. 

7 Reprinted from Bulletin of the Natural History Society of New Bruns- 
wick, No. XIX., 1901. 
