BRACHIOPODA. 
63 
narrow, divergent muscular grooves, bordered on their anterior edges by thick¬ 
ened ridges, both having the shape of a broad inverted V. 
In the brachial valve the character of the hinge-plate has not been ascer¬ 
tained, but was probably simple, and it was supported by a median septum 
traversing about one-half the length of the valve; on either side of this septum 
are the lateral members of the adductor impression. The crura are short and 
straight; the primary lamellae are attached to them by a subrectangular curve 
and pass outward just within the margin of the valve. The spirals are but 
slightly elevated and have their apices directed outward toward the lateral 
slopes of the opposite valve. The ribbon makes but three or four turns, and 
its outer anterior edges are quite coarsely fimbriated. The loop is situated 
anteriorly, taking its origin near the upward turn of the primary lamellse; it 
is directed upward and backward, the lateral processes meeting at or just behind 
the center of the interior cavity. From the point of union proceeds a short, 
simple process, which does not make an angle with the rest of the loop. 
We have had the opportunity of verifying most of these characters by 
cuttings of specimens obtained from the Gotland limestone. No congeneric 
species was known to Mr. Davidson, and, as far as our knowledge goes, there 
is no representative of this structure in the American palaeozoic faunas. 
The external resemblance of Dayia navicula to the Atrypa bisulcaia of the 
Trenton limestone, is worthy of remark, and the differences between the two 
in the structure of the brachidiurn are actually slight, though in one the spirals 
are everted and in the other they are inverted. Further notice is taken of 
these differences in the discussion of the genus Cyclospira. 
Genus HINDELLA, Davidson. 1882. 
PLATE XLI. 
1862. Atliyris, Billings. Palieozoic Fossils, vol. i, p. 144, fig-. 121; p. 145, fig-. 122. 
1863. Athyris, Billings. Geology of Canada, ji. 317, fig. 331. 
1882. Hindella, Davidson. British Silurian Brachiopoda, Supplenaent, p. 130. 
1885. Meristella, Foer.ste. Bull. Denison University, vol. i, p. 88, pi. xiii, fig. 2. 
Mr. Davidson has found that the meristelloid species described by Billings, 
from Junction Cliff, Anticosti (Division 1 of the Anticosti group), as Athyris 
