ORXnOCEKATIDJE. 
17 
surface into square cancellations. The septa have a convexity of | 
the diameter, and appear to cut the ribs on the upward slope; The 
siphuncle is central and small. {Blal'e.) 
Remarks. “ The statement that 0. ibex occurs in the Lower 
Silurian is doubtless founded on examples of this species (M‘Coy, 
British Pal. Loss. p. 319). The ribs, however, have not the 
separateness of those of 0. tenuianmilatum, which is the species 
meant ; and though in some the transverse lines are scarcely dis- 
cernible, in other associated examples they are equal to the longi- 
tudinal, which is only the case in the young of !M‘Coy’s species. 
Moreover, the separation of the septa by two rings is a feature 
which unites the Cumbrian examples to those from Ireland. 
0. diJicretum, Barrande, from Etage F, is very closely allied, but 
the ribs are much more pronounced and separate, and the cancella- 
tion is never eqnal in the two directions, while the rate of increase 
is less.” {Blahe.) 
Horizon. Upper Bala. 
Locality. Cynwyd, Merionethshire* 
Two specimens presented by J. E. Lee, Esq., F.G.S. 
Orthoceras striatissimum, Salter. 
I860. Orthoceras striatissimum, Salter, in Paheont. of Niti in tlie 
Northern Himalaya, by Salter and Blanford, p. 16, pi. ii. f. 4. 
Char. Broad-oval in section, very slowly tapering, without 
rings or any inequalities except very fine transverse strim. 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 curving 
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. Siphuncle ? 
“ In the oblique fine striae and slowly tapering form, this resembles 
a great many Silurian species. 0. tenuicinctam \elon(jatocinctum\ 
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 indi- 
cated by the stronger rings ; but this is somewhat uncertain.” 
Horizon. Lower Silurian (Ordovician ?). 
Locality. Chorhoti Pass (17,000 feet), Himalaya Mountains. 
Represented by one of the examples figured by Salter. 
c 
