16 
SILURIAN 
aspect so much recalls several common Silurian shells. The 
0. Ibex of the Silurian System is especially like it, and as 
there is a Thibetan antelope (the Kemas) with horns of the 
Ibex type, I have adopted a specific name suggested by Colo¬ 
nel Strachey. 
Diameter 5 lines, very little tapering, and with an oval sec¬ 
tion. Rings oblique, not waved, and scarcely 2 lines apart, 
blunt, prominent, not so broad as the spaces between them. 
Surface much abraded, but showing traces of longitudinal stria? 
as in the English species to which it is allied. Neither septa 
nor siphon are visible in our solitary specimen. 
Locality. —Kalajowar, 16,000 feet. (No. 1757.) 
Fragments of two other smooth species occur. One is g^th 
of an inch diameter, with somewhat oblique septa and the 
siphon eccentric. It was found at Upper Rimkin in grit. 
The other, from Chorhoti Pass (1744), is doubtful, and 
may be the young of either of the other species—for it is 
only yyth of an inch diameter. 
THECA LINEOLATA. 
. Plate 2, fig. 6. 
T. recte trigona, clorso curvo, lateribus planis tenuissime striatis. 
Strife longitudinales asperse, sequales,—incrementi nullao. 
About two-thirds of an inch long, and scarcely 2 lines broad, 
regularly tapering, without any transverse rugae or striae of 
growth, but covered with close sharp longitudinal threads, not 
wider than the interstices. Section rather more than a right- 
angled triangle (100° to 110°) ; the ventral surfaces flat,— 
the dorsal surface curved (as shown by the section, for the 
specimen is covered by stone on the dorsal region, and no part 
of that surface is visible). One specimen only was found. 
Locality .—Chorhoti Pass. (No. 1754.) 
