1M^]CTEN. l(i!» 



licnKirJrs. — ^riic rioht valve is loss common than tlio left, 'i'lic state of presei'- 

 vation of the shell, and consequently the appearance of the ornamentation, varies 

 a good (leal. 



Type. — From Blackdown ; in the Bristol Museum. 



Disfrihnfinii. — Blackdown Greensand (Bed 10). Recorded by Downcs (1882) 

 from Ilaldon, and by Jukes-Browne (1900) from the Upper Greensand of Lulworth 

 and Warminster. 



PjiCTEN (CiiLAMYs) siTjiA( 'UTds, Laiii<iirl; iSl!). Plate XXXI, figs. 7 n,h, Sr/— r, 9. 



l8l'J. Pecten SUI5A.CUTUS, LamarcJc. Auiiu. sans Vert., vul. vi, p. 181. 

 1836. _. -_ _ Ibid., ed. 2 (by Desliayes aud Milne- 



Edwards), vol. vii, 23. 158. 

 1847. — ~ A. cVOrhhjnij. Pal. Fran?. Terr. Grot., vol iii, p. f.nS, 



pi. ccccxxxv, figs. 5 — 10. 

 ? — — Brongniarti, a. (VArrJilac. Mem. Soe. geol. de France, ser. 2, 



vol. ii, p. 310, pi. xvi, fig. 4. 

 1850. — — H. B. Geiuitz. Das Quadersandst. oder Kreidegeb. 



in Deutschland, p. 183. 

 1870. — SUBACUTUS, F. J. Pidet and G. Camjnche. Foss. Terr. Cvct. Ste 



Croix (Mater. Pal. Suisse, ser. 5), pp. 214,218. 

 1872. — — //. B. Gtliilh. Das Elbthalgeb. in Sacliseu (Paliconto- 



grapliica, vol. xx, pt. 1), p. l'J5, pi. 

 xliv, fig. 5. 

 1877. — — A. J. Jukes-Browne. Quart. Journ. Geol. Soe., vol. 



xxxiii, p. 501. 

 1896. — — _ and W. Hill. Ibid, vol. Iii, p. 151. 



Dct>cri2)tioii. — Shell ovate, pointed dorsally, much higlier than long, nearly e(|ui- 

 lateral, convexity small. Apical angle al)ont b'O". 



Right valve with aljout twenty-three strong ribs, which are straight or sliglitly 

 curved, and have usually sharp summits, l)ut are sometimes rounded ; the grooves 

 separating the iil)S are broad, with rounded or angular bases. Near the anterior 

 and })osterior margins the ribs are rather smaller; near the umbo they are often 

 more rounded than elsewhere. Both ribs and grooves are crossed l)y numerous, line, 

 close-set, Avavy, laminar ridges, which are more regular and distinct near the lunbo 

 than ventrally. The I'iljs usually l)ear along their sunnuits many scaly knobs or 

 short spines, which are often distributed at fairly regular intervals ; sometimes these 

 scaly spines are absent over part or almost the entire shell. Anterior ear large, 

 with a deep sinus ; growth-ridges well-marked, radial I'ilis indistinct. Posterioi- ear 

 nuich smaller, triangular, with radial ribs. 



22 



