10 
NAFTILOIDEA. 
Ophidioceras articulatum, J. de C. Sowerby, sp. 
1839. Lituites artieulatus, J. de C. Sowerby, in Murchison’s ‘ Sil. Syst.’ 
pt. ii. p. 622, pi. xi. f. 5 (not f. 7). 
1854. Lituites Ihex, Salter, in Murchison’s ^ Siluria,’ pi. xxxi. f. 6. 
1873. Lituites artieulatus^ Salter, Cat. Cambr. and Sil. Foss. p. 174. 
1882. Ophidioceras articulatum,BhikQ, British Foss. Ceph. pt. i. p. 230, 
pi. xviii. ff. 14, 14 a, 15. 
[ Not 1852. Lituites artieulatus, M^Coy, British Pal. Foss. p. 323.] 
Char. “ The rate of increase, as measured, ranges from 1-43 
to 1’29 ; but from the compression to which the specimens have been 
subjected, these measurements are seldom very reliable. The inner 
whorls are always just in contact — till the body-chamber, which 
leaves the coiled part at a diameter of from 9 to 14 lines, and con- 
tinues straight for f the greatest diameter. In an obscure fossil 
referred to this species from the Wenlock Shale, the uncoiled part 
reaches twice this distance. There is no sign in any of the slightest 
want of symmetry. The ribs are always direct, more or less sepa- 
rate, with a slightly backward direction towards the outside, from 
26 to 28 per whorl. The front had a flattened band along it as 
shown by two smooth parallel lines in more than one example. The 
flner ornaments are parallel lines of growth, and the surface is occa- 
sionally pitted. The section wheu unflattened is uniformly rounded. 
The body-chamber consists of some part of the coiled portion ; the 
ribs die out towards the aperture, which is not seen to be contracted. 
The septa are more remote than the ribs, being but 14 per whorl in 
the earlier part. The siphuncle is only seen in one example in the 
Wenlock Limestone, where it is nearly external, being preserved 
after the decay of the shell. The diameter is never more than 1^ 
inches. The straight ribbing and the band along the front easily 
distinguish this from previously described British forms ; but it is 
very similar to some of the other Opliidiocerata figured by Barrande 
on plate xlv. of his Silurian Cephalopods (Syst. Sil. de la Boheme , 
vol. ii. pt. i. 1867), with none of which, however, it exactly agrees, 
but is nearest to 0. tenerum or 0. simplex. The contracted aperture 
has not, however, been seen in British examples.” {Blahe.) 
UemarTcs. This is rather a rare species, and examples found in the 
British rocks are poorly preserved. A specimen in the Collection 
from the Wenlock shales of Nantglyn, Denbighshire, may possibly 
belong to the present species, but it is too much distorted for certain 
recognition ; it shows the straight piece, and exhibits obscurely the 
characteristic transverse ribbing. 
Horizon. Wenlock Shales, Lower Ludlow. 
