164 
PROCEEDINGS COTTESWOLD CLUB 
igi6 
Pholadella McCoyi, sp. nov. [PL VII., fig. 3; PI. VIII., fig. 4.] 
Description . — Shell oblong, inequilateral, subvcntricose anteriorly 
highest at be^ik ; anterior end rounded ; posterior end obliquely truncatefl 
above, subacute below ; inferior margin nearly straight, very slightly conve.x, 
parallel to hinge-line, meeting posterior margin at 6o° or rather less ; hinge- 
line straight, about three-fourths the length of shell, meeting posterior margin 
at an obtuse angle. Beak prominent, high, swollen, obtuse, rounded, some- 
what incurved, rising well above hinge-line, situated at about one-fourth the 
length of shell from front end. Umbonal ridge well marked, sub-angular, 
oblique, running diagonally to posterior-inferior angle ; area between it and 
hinge-line narrow, small, somewhat flattened or depressed. Surface of shell 
with anterior two-thirds marked by regular fine equidistant thread-like con- 
centric lines ; posterior third and umbonal ridge ornamented with fifteen to 
twenty fine stx'aight radial lines, to which the concentric lines are inclined 
at 75°-9 o°. 
Dimensions : Length, 15%. 
Height, 10^. 
Horizon and Locality. — From near the top of the Ludlow 
beds in the Quarry 150 yards South-East of Pen-y-parc. 
Remarks. — This species is well characterised, though none 
of the Usk specimens are quite perfect. It seems to resemble 
the American Pholadella radiata, Hall,* of the Hamilton and 
Chemung formations, rather than any Silurian species from 
England, except perhaps the shell referred by McCoyi to 
Nuetdites post-striatus Emmons.^ 
Orthonota rigida Sowerby. 
Remarks. — In spite of a large number of British species of 
Ordovician and Silurian lamellibranchs being referred to the 
genus Orthonota, American geologists appear to regard it as 
limited to the Devonian. The type of the genus is 0 . undidata 
Conrad, and the strict definition of the genus given by HalP 
would exclude many, if not all, of the forms which commonly 
are ascribed to it in this country. Further work is required 
before a conclusion can be reached in this matter. Only one 
example of Orthonota rigida Sow. occurs in Mr Gardiner’s 
collection from the Usk district. 
Horizon and Locality. — Ludlow beds seen in the quarry 
by the side of the road leading East from Sluvad, about half 
a mile from the farm of that name. 
1 Hall, PaleBoiit. N.Y., vol. v., Lamellib. ii., p. 469, pi. Ixxviii., figs. 15-21. 
2 McCoy, Syn. Pal. Foss. Woodw. Mus., p. 286, pl. i K, fig. 6. 
5 Emmons, Geol. Report, i8.|2, p. 399, fig. 4. 
4 Hall, Palaoiit. N. York, vol. ^•., pt. i, Lamcllibr., ii. (1885), p. xlv. ; Eastman-Zittel, Text- 
book of Palaeoiitology, 2nd edit., vol. i, 1913, p. 462. 
