DR. G. J. HINDE ON RECEPTACULITIDA, 843 
This well-known species grows in flattened disk-like expansions, 
which, when entire, are from 100 to 200 millim. in diameter. The 
nucleus or commencement of growth is a small conical projection 
on the under surface and formsa small piton the upper. The walls 
vary in thickness from 4 millim. in the centre to 12 millim. at the 
periphery of the organism. The spicular plates of the outer surface, 
with the exception of those immediately round the nucleus, vary 
from 3 to 5 millim. in width, and the horizontal rays are somewhat 
more than half the width of the plates. The vertical rays vary 
from 1 to 2 millim. in thickness. The inner or upper plate is about 
i millim. in thickness; the vertical canals by which it is perforated 
are about 1 millim. in width. The upper or outer surface of this 
plate is frequently irregularly furrowed by open canals. 
In the massive limestones at Pauquettes Rapids on the Ottawa, 
the species is very abundant and is partly composed of silica and 
partly in the state of crystalline calcite. When freed from the 
matrix by dilute acid, the structure is more clearly shown than in 
any other example of the genus. The specimens from Illinois, &c., 
are generally in the condition of casts. This species was referred 
by D. Dale Owen to Coscinopora sulcata, Goldf. =R. neptunr, and 
Hall, in 1861, proposed to change the name to 2. Oweni. Previously 
to this, however, Salter described and figured the species and gave 
it the name which it now bears. Salter suggested that A. Neptuni? 
Hall,* from the Trenton limestone of Carlisle, Pennsylvania, might 
also belong to the same species, but from Hall’s figures it appears to be 
distinct, and it is moreover stated to be suborbicular or hemispherical. 
The examples from Illinois and other Western States are usually of 
somewhat greater diameter than those from the same horizon in 
Canada, but from a comparison of specimens from these different 
places I am unable to detect any differences which would justify 
regarding them as distinct species. Their external aspect is, how- 
ever, strikingly dissimilar owing to their different states of fossili- 
zation. 
Distribution.—Lower beds of the Trenton limestone: Pauquettes 
Rapids, Ottawa River, Canada. Galena limestone: Galena, Dixon, 
Illinois ; various localities in Wisconsin and Iowa. Lower Silurian: 
Cape Louis Napoleon ; Igloolik, Arctic regions. 
RECEPTACULITES ORBIS, Hichwald. 
1860. Receptaculites orbis, Hichw. Leth. Ross. vol.i. p. 428, t. 27. 
f.1; cf. Hscharites forniculosus, Schloth. Petrefactenkunde, 1820, 
. 043. 
: 1858. Receptaculites orbis, Fr. Schmidt, Silur. Form. von Ehst- 
land, &c., p. 232. 
1875. Receptaculites orbis, Gumb. Beitr. pp. 39, 41. 
1880. Receptaculites orbis, F. Romer, Leth. Pal. Th. 1, p. 289. 
1882. Receptaculites orbis, T. R. Jones, Cat. Foss. Foram. Brit. 
Mus. p. 2. 
Flattened disks from 80 to 150 millim. in diameter. The walls 
* Pal. New York, vol. i. p. 68, t. 24. f. 3. 
