VOL. XIX. (2) 
USK INLIER (.\PPEXU 1 X) 
1 61 
Pteronitella inexpectata, sp. nuv. [PI. VII., fig. i.] 
Description.— HheU narrow, elongated, nearly tliree liine.s as long as high, 
compressed, flattened, with very slightly con ve.\ undefined body, most swollen 
near beak; hinge-line long, straight, equal to length of shell. Anterior ear 
very small, flattened, not distinctly marked off from body nor projecting on 
margin. Posterior ear very lai'ge, long, narrow, elongated, triangular, less 
than one half the height of shell on posterior margin. Beak inconspicuous, 
obtuse, low, not rising above hinge-line, and situated close to its anterior 
end. Anterior end of shell blunt, steeply rounded, meeting hinge-line at 
right-angles, passing down into long gently arched inferior margin curving 
up posteriorly at about 30° towards hinge-line, but meeting it at about 45° ; 
slightly excavated behind posterior ear, but otherwise regularly curved 
and not sinuated. Surface of body smooth, e.xccpt for a few marginal 
concentric lines anteriorly ; posterior ear ornamented with twenty to 
thirty fine straight radial ribs with four to five deeper and stronger equi- 
distant interspaces between them, and all crossed by rather weaker trans- 
verse lines concentric with the posterior margin at somewhat iiTegular dis- 
tances apart giving a cancellated appearance to the surface. 
Dimensions : Length . . . . . . . . . . So-o 
Height (at middle) .. .. .. 31-0 % 
Width of posterior car on margin . . 13.5 % 
Horizon and Locality . — Ludlow beds : just behind Parish 
Room, north of Llanbadoc Church. 
Remarks . — This new species, of which only one right valve 
is known, must be referred to the genus Pteronitella Billings," 
to which Pt. condor Salter^ from the Lower Ludlow of Dudley 
also belongs. It somewhat resembles Pt. oblonga Billings,^ 
from Arisaig, Nova Scotia, and especially may be compared 
with Pt. passer Clarke,'^ and Pt. hirundo Clarke, * from the 
Helderberg formation. In the latter species, Clarke says the 
radial lines on the shell are obsolete on the right valve except 
on the posterior wing. The same limitation of the ornament 
is noticeable in Palceopinna flahellum Hall,^ from the Oriskany of 
New York and Gaspe — a shell which seems very similar except 
for the more terminal beak and the complete obsolescence of 
the anterior ear. The genus Pteronitella appears to be charac- 
teristic of the higher Silurian and the lower part of the De- 
vonian. The type chosen by Billings is Avicula retroflexa 
Hisinger, but the first species described and figured is Pteroni- 
tella venusta Billings,^ from the Upper Silurian of Arisaig, 
Nova Scotia. 
1 Billings, Palaeoz. Foss. Canada, voJ. ii., pt. 1 (1874), P- 
2 Reed, Geol. Mag., Dec. IV., vol. ix. (1902), p. 147, pl- vii., figs. 6, 7- 
3 Billings, op. cit., p. 143, pl. 9, fig- 7 - , ^ 
4 Clarke, Mem. New York State Mus. No. 9, pt. 2 (1908), p. 30, pl. 4, figs. 12-14. 
5 p. 29, pl. 4, figs. 8-11. 
6 Hall, Palaeont. N.Y., vol. 5, pt. i (1884), p. 240, pl. 87, fig. .< ; Clarke, op. at., pt. i., pp. 159, 
233, pl. 21, figs. 1-5. 
7 Billings, op. at., p. 142. pl- 9. fig*>- 5, 5®- 
M 2 
