BBACKIOPODA AND BRYOZOA. 
45 
and it is evenly convex over the whole shelly except a narrow 
keel which runs down the middle line, and which is not 
always present. The front is deeply indented,—hut not raised 
by the sinus, which is of a broad lanceolate form. 
The lines of growth are conspicuous (and somewhat rugged 
near the front), and there are short interrupted longitudinal 
striae (not ribs) covering the whole surface, but they are very 
obscure in most of the specimens. 
Muscular impressions very distinct, rounded, separated by 
a low but well-marked ridge, and reaching but a short way 
down the shell. 
Locality .—Chorhoti Pass. (1743, 1744.) 
ORTHIS —Other Species. 
Besides these species, there are several which, though 
plentiful enough, and presenting characters sufficient to 
distinguish them from those above described, are not suffi¬ 
ciently perfect to make it worth while to figure or give them 
names. We must wait (perhaps a long while—for it is not 
given to every one to geologize in perpetual snow) for better 
material. Enough has been done to show how nearly allied 
this Tibetan fauna was to our own in Carodoc times—and 
yet its specific distinction was complete. 
BRYOZOA OR POLYZOA. 
The prominent Silurian forms of the group appear to have 
been precisely of the same nature in the Indian as in the 
European areas. The genus Ptlloclictya , under forms so like 
those of our Caradoc rocks that one might be taken for the 
other, is the prevalent form in Britain, and, as might be 
expected, is the first one that occurred to the search of Colonel 
Strachey. And, as in our own slate rocks, the narrow 
bifurcating forms and broad foliaceous species are found 
together. 
