Vol. 58. | JURASSIC OF THE SOUTH WALES DIRECT LINE. 725 
(g) The Oxynotus-Beds. 
Proceeding eastward, we found the section completely obscured, 
until we reached a point about 200 yards from the mouth of the 
tunnel; here the cutting has vertical walls, and the beds are well 
expesed. They consist of a series of shales and thin limestone-bands, 
precisely similar in character to those of the Semzcostatus-Beds 
already described. At first the dip is very inconsiderable, but there 
is a marked easterly dip in the neighbourhood of the tunnel-entrance. 
The beds of this series contain few fossils, though crushed 
ammonites are not uncommon in the shales. They are doubtfully 
referred to the species Ammonites densinodus, Quenst., but the 
absence of any solid fragments that clearly exhibit the rim renders 
accuracy of determination impossible. 
Avicula (Oxytoma) inequivalvis, Sow. is not uncommon. 
(h) The Armatus- and Jamesoni- Beds. 
Just at the mouth of the tunnel, these beds are well exposed in 
the steep bank on the south of the line. 
Lithologically, they consist of thick shales separated by thin 
limestone-bands precisely similar in general character to the beds 
below. Palzontologically, the beds at the base contain numerous 
badly-preserved ammonites, the commonest form being a species of 
Deroceras closely allied to D. armatus ; while Ammonites carusensis 
is not uncommon, in a pyritized and somewhat crushed state. 
Throughout the series a crushed form, probably Ammonites densi- 
nodus, 1s common in the shales. 
Towards the top of the section fossils are very common, though 
as a Yule poorly preserved: we have determined the following 
species :— 
Ammonites Scipionianus (2?) d’Orb. | 
Belemnites penicillatus, Sow. | B. aff. paxillosus, Schloth. 
B. clavatus, Blainv. | Rhynchonella aft. Thalia, d’Orb. 
B. longissinus, Mill. | Waldheimia (Zeilleria) numismalis, 
B. acutus, Miil. |} Lam. 
Belemnites aff. grandevus, Phil. 
Paleontological Notes. 
The determination of the belemnites, as is usually the case with 
this group, was a mattcr of considerable difficulty. This difficulty 
arises from three main causes: firstly, the fact that, while we have 
to rely almost entirely upon the shape of the guard and the nature 
of the apical grooves, the mutations of form are continuous and 
ulmost endless, and the extent to which a groove is pronounced may 
vary from a deep rut to the most inconspicuous depression ; secondly, 
the difference of opinion among students of the group as to the exact ” 
connotation of the specific names; and lastly, the fact that there are 
undoubtedly very many forms, or stages in mutation, which require 
new names. For these reasons, we have been content in most cases 
to employ the name given, in the monograph on belemnites published 
by the Paleeontographical Society, to the species most like the one 
that we had to determine. 
