62 
PAET II. 
DEVONIAN SPECIES. 
Division — PKOTOZOA» 
Class — KIIIZOFODA. 
Order— smmWA. 
Genus—AVXI12E0GYATE.V8, Billings. 
Among the genera comprised in the order Spongida, without doubt 
one of the most important is that which Mr. Billings has discovered in the 
Potsdam Sandstone of Canada, and which he has described under the name of 
Arcli(EOcyat]ius. 
It is to this genus that I refer, without, however, being quite certain 
that it belongs to it, a species of which Mr. Clarke has sent me two specimens. 
But as their preservation leaves much to be desired, it is impossible to be 
more definite about them. As to the species, it appeared to me different to 
any with which I could compare it, and it is described under the following 
name : — • 
Archmocyathus ? Clarkei, L. G. de Koninch} 
PI. II, %. 1. 
As I have at my disposal only imperfect specimens of this species, it is 
not easy to define it. It appears to be composed of a layer only eight to ten 
millimetres thick, but fairly well developed in height and breadth, and 
irregularly folded, thus forming fairly deep cavities ol: very variable shape. 
The outer wall of the sponge mass, properly speaking, is often furnished with 
irregular protuberances, two to three millimetres in diameter at their base 
and pierced by small openings which are easily apparent, characters which 
agree fairly well with those of ArclKBocyathus. I have not been able to 
examine the inner surface. The part between the two surfaces has a more 
or less irregular spongy structure, which, in transverse sections has the 
appearance of ridges perpendicular to the surfaces. By removing the outer 
' [Fide G. J. Hinde, Quart. Journ. Geol. Soc., 1889, XLV, p. 127. — W.S.D.] 
