VOL. XIX. (2) 
USK INLIER (APPENDIX) 
165 
Orthonychia, sp. [PI. VIIL, figs. 17, 17a.] 
Remarks . — The genus Orthonychia' does not appear to 
have been recorded from the British Silurian rocks, but there 
is one internal cast of a shell from the Usk district in Mr 
Gardiner’s collection which must be referred to it rather than 
to Platyceras or any other genus. 
The shell forms a tall, acutely-pointed conical cap, 
slightly unsymmetrical, with the apex bent backwards so as 
to overhang the base. The lateral portions are not ridged 
except for a weak angular keel on each side, which starts from 
the apex and dies out towards the base ; the back is well 
rounded ; there is a slight median angulation of the posterior 
concave side, and between this keel and the lateral keels the 
surface is somewhat flattened or excavated, especially near the 
apex. The apertural basal margin is gently sinuated, having 
a broad shallow rounded anterior and posterior emargination 
and a broad slightly dependent rounded lateral lobe on 
each side. The back or convex arched portion of the shell 
is marked by gently curved lines concentric to the anterior 
marginal sinus. The apical angle is rather less than 30°. 
Height of apex from base . . . . about 25% 
Transverse diameter at base . . . . ,, 28 ,, 
Antero-posterior diameter at base . . ,, 32 ,, 
Horizon and Locality . — Near the top of Wenlock Shales 
in the track leading West from the Usk railway, 300 yards 
North of Tynewydd. 
pROETUS Stokesi Muixhison, var. nov., bellula. 
[PI. VIII., figs. 5-11.] 
Desoviption. — Head-shield semi-oval, with its genal angles produced into 
stout spines having about three-fourths the length of the head-shield. Glabella 
short, convex, sub-oval, widest near base, narrowing anteriorlj'- to blunt 
sub-truncate end, not reaching marginal furrow ; marked with three pairs 
of lateral furrows ; first pair of furrows faint, short, horizontal, situated at 
about one-fourth the length of the glabella from the front-end ; second pair 
stronger, deeper, rather obliquely inclined backwards and extending in- 
wards about one-fourth the width of the glabella ; third pair not connected 
with the axial furrows, arising a short distance within them as deep depressions 
at about two-thirds the length of glabella from its front end, continued very 
obliquely backwards as deep curved furrows weakening posteriorly to meet 
1 Peruer, Syst. Silur. Bohemc, vol. iv.. Tome iii. (lyii), pj>. 2 -, 9.2. 
