MOLLUSCA. 
15 
This species puts one in mind greatly of the L. (Troc/wliies) 
ammonias of Conrad, a Lower Silurian species from North 
America, and belongs to the same division of the genus. It 
differs in being much less compressed from back to front. 
Locality .—Chorhoti Pass, 18,200 feet high. (No. 1733.) 
ORTHOCERAS STRIATISSIMUM. 
Plate 2, fig. 4. 
O. parvum, vix conicum, striis transversis subtilibus asperis, (nou- 
nullis prominulis) obliquis, utrinque undulatis. Septa—? Siphon ? 
Broad-oval in section, very slowly tapering, without rings 
or any inequalities except very fine transverse striae. These 
striae are oblique from back to front, with a slight double wave 
on the side, so that the curve is downward from the back to the 
middle of the side, and thence gently upward again before curv¬ 
ing downward over the front. The striae are fine and elevated 
threads,—in some specimens every seventh or eighth is more 
prominent than the rest—in other specimens the prominent 
ones are less frequent. 
In the oblique fine striae, and slowly-tapering form, this 
resembles a great many Silurian species. 0. tenuicinctum , 
Portlock, a Lower Silurian species from Ireland, is especially 
like ours. Even the wave of the striations (not correctly 
represented in our figure) is but a little more decided than is 
usual in the smoother species. The septa are not plainly seen, 
unless they are indicated by the stronger rings ; but this is 
somewhat uncertain. Siphuncle ? 
Locality .—Chorhoti Pass, 17,000 feet. (Nos. 1743-4.) 
ORTHOCERAS KEMAS. 
Plate 2, fig. 5. 
O. modicum, subcylindricum, annulis obliquis remotiusculis lin- 
eisque longituclinalibus ornatum. Septa ? 
A fragment only 1£ inch long, and about one-third of an 
inch diameter, is all we have of this species, which by its 
