PECTEN. 189 
1841. Pecren Beavers, F. A. Rimer. Die Verstein. d. nord-deutsch. Kreidegeb., 
p. 54. 
1850. — ? Beaver, A. d'Orbigny. Prodr. de Pal., vol. ii, p. 169. 
— — Juaosus, J. de C. Sowerby, in F. Dizon. Geol. Sussex, p. 347 (p. 
382, ed. 2), pl. xxviii, fig. 26. 
1854. = Breavert, J. Morris. Cat. Brit. Foss., ed. 2, p. 175. 
1863. _ ~~ A. v. Strombeck. Zeitschr. d. deutsch. geol. Gesellsch., 
vol. xv, p. 108. 
1870. -- — F. J. Pictet and G. Campiche. Foss. Terr. Crét. Ste. Croix 
(Matér. Pal. Suisse, ser. 5), pp. 214, 218. 
1871. — — FI. Stoliczka. Paleont. Indica, Cret. Fauna 8S. India, 
vol. iii, p. 428. 
Deseription.—Shell large, thin, oval or nearly circular; height usually slightly 
greater than length; margins evenly rounded except at the junction with the 
ears. Valves compressed, nearly equal, slightly mequilateral. Apical angle large, 
from 118° to 125°. Kars long, low, a little unequal. 
Right valve with broad radial ribs, which have sharp and sometimes slightly 
irregular summits and gently sloping sides; there are also similar smaller ribs, 
which do not reach the umbo. The ribs are smaller anteriorly and posteriorly. 
The surface of the valve is ornamented with fine, close-set, concentric, linear 
ridges, and sometimes with radial ridges. Anterior ear with a well-marked sinus, 
ornamented with scaly ribs except near its junction with the valve. Posterior 
ear smaller, outer angle nearly a right angle ; surface with ribs, sometimes obscured 
by concentric lamelle. 
Left valve with about seventeen main ribs, which are narrow, elevated, and 
sharp, sometimes slightly serrate at the summits; separated by broad furrows. A 
smaller rib is often introduced in the middle of the furrow at a distance from the 
umbo, and on the sides of the ribs other still smaller ribs may occur. Anteriorly 
and posteriorly the main ribs become smaller. The ribs and furrows are crossed 
by many fine, close-set, regular, concentric ridges, which are seen most distinctly 
in the furrows. Anterior ear a little more elevated than the posterior; both with 
radial ribs and sharp outer angles. 
Measurements : 
(1) (2) (3) (4) (5) (6) 
encthms) cl = 86. 88: 106° 96>.) 109 cam. 
Hohtueemol me oo; 1 LOLs 1060 9dr. NOD sg 
(1, 2) Chalk Marl, Folkestone. 
(3) Pp ». Meldreth. 
(4, 5) Totternhoe Stone, Burwell. 
(6) H. subglobosus zone, Cherry Hinton. 
Affinities. —I?. depressus, Goldfuss, seems to be scarcely distinguishable from 
l’. Beaveri. The specimen figured by Goldfuss as 2. Beaver does not show the 
