50 
SILUllIAN AND 
no where known in the primordial fauna) existed under much 
the same forms in the Asiatic area as our own. Of the few 
brought home in this collection, only one or two are sufficiently 
perfect to name. The largest and commonest is a species of 
Cliatetes , or what appears to be so—of a size unusual in Silurian 
rocks and much more nearly resembling those of the mountain 
limestone. I have named it after the hoof of the Thibetan 
ox, the Yak. 
CHiETETES ? YAK. 
Plate 5, figs. I, 2. 
C. pedalis, hemispheric;!, tumida, bnsi perrugata, cellulis fibrosis ra- 
diantibus liexagonis, uncise latis, rectis, contiiiuis. 
A large tumid hemispheric coral; sometimes a foot across ; 
’ which I cannot but regard as a species of Chadeies , allied to 
the Russian carboniferous species, C. radians. When broken, 
however, it does not show the character usually ascribed to the 
genus, viz.: the open fracture of the tubes. On the contrary, 
the surface of the long fibrous cells is exceedingly well pre¬ 
served, and the coral fractures readily along these, exposing 
the surface of the walls—as in Favosites. But I can see no 
trace whatever of pores. 
The mass is hemispherical; the base roughly and concentri¬ 
cally rugose. The fracture exposes radiating straight tubes of 
a fibrous appearance; and the surface shows scattered clusters 
of large cells amongst those of ordinary size—the larger ones 
G \ F tli of an inch diameter, the smaller -jiyth. The tubes are 
hexagonal, with somewhat wavy angles (but not produced 
into projecting tubercles) and show plainly the numerous 
(gently concave) diaphragms, very regularly placed at about 
the diameter of the tube apart. They run in paralled bands 
—at the same horizon all over the coral—and only interrupted 
at intervals by the varies of growth which are from |rd of inch 
to half an inch apart, and very regularly concentric. 
The cells on the surface are too much worn to be sure of the 
character of their edges. They may very probably be smooth 
(as in our figure). 
