PECTEN. 169 
Remarks.—The right valve is less common than the left. he state of preser- 
vation of the shell, and consequently the appearance of the ornamentation, varies 
a good deal. 
Type.—From Blackdown ; in the Bristol Museum. 
Distribution.—Blackdown Greensand (Bed 10). Recorded by Downes (1882) 
from Haldon, and by Jukes-Browne (1900) from the Upper Greensand of Lulworth 
and Warminster. 
Prcren (Cutamys) susacutus, Lamarck, 1819. Plate XXXI, figs. 7 a,b, 8a—e, 9. 
1819. Prcren susacurus, Lamarck. Anim. sans Vert., vol. vi, p. 181. 
1836. _— — Ibid., ed. 2 (by Deshayes and Milne- 
Edwards), vol. vii, p. 158. 
1847. — = A. d'Orbiqny. Pal. Frang. Terr. Crét., vol. ii, p. 605, 
pl. ceeexxxv, figs. 5—10. 
i= = Broneniarti, A, d’Archiac. Mém. Soc. géol. de France, ser. 2, 
vol. ii, p. 310, pl. xvi, fig. 4. 
1850. - — H. B. Geinitz. Das Quadersandst. oder Kreidegeb. 
in Deutschland, p. 183. 
1870. —  susacurus, F. J. Pictet and G. Campiche. Foss. Terr. Crét. Ste 
Croix (Matér. Pal. Suisse, ser. 5), pp. 214, 218. 
1872. — — HW. B. Geinitz. Das Elbthalgeb. in Sachsen (Paleonto- 
graphica, vol. xx, pt. 1), p. 195, pl. 
xliv, fig. 5. 
1877. a — A. J. Jukes-Browne. Quart. Journ. Geol. Soe., vol. 
xxxil, p. 501. 
1896. _ -- -- and W. Hill. Ibid, vol. lui, p. 151. 
Description.—Shell ovate, pointed dorsally, much higher than long, nearly equi- 
lateral, convexity small. Apical angle about 80°. 
Right valve with about twenty-three strong ribs, which are straight or slightly 
curved, and haye usually sharp summits, but are sometimes rounded; the grooves 
separating the ribs are broad, with rounded or angular bases. Near the anterior 
and posterior margins the ribs are rather smaller; near the umbo they are often 
more rounded than elsewhere. Both ribs and grooves are crossed by numerous, fine, 
close-set, wavy, laminar ridges, which are more regular and distinct near the umbo 
than ventrally. The ribs usually bear along their summits many scaly knobs or 
short spines, which are often distributed at fairly regular intervals ; sometimes these 
scaly spies are absent over part or almost the entire shell. Anterior ear large, 
with a deep sinus ; growth-ridges well-marked, radial ribs indistinct. Posterior ear 
much smaller, triangular, with radial ribs. 
