PECTEN. 181 



a pointed granule wliere tlie}^ cross the radial ril)s ; near the ventral border the ribs 

 are often very closely placed. Ears triangular, with a few growth-lines ; the 

 anterior Avitli granular ribs and nearly rectangular outer angle, the postei'ior snialler 

 and with obtuse outer angle. 



Measurements : 















(1) 



(2) 



(3) (4) 



(5) 



(6) 



(7) 



(8) 



Length . 39 



. 38 



. 33 . 32 . 



30 . 



28 . 



, 20 



. 20 mm. 



Height . 45 , 



. 44 



. 37 . 35 . 



35 . 



31 . 



31 . 



, 23 „ 





(1- 



-8) B. mucronatu zone, 



uear Nor 



wicli. 







Affinities. — In form, and in the possession of similar radial and concentric 

 ornamentation, this species resembles some of the varieties of P. cretosus, but is 

 easily distinguishable by the stronger radial ridges, etc. 



liemarhs. — The differences in the appearance of the ornamentation in this 

 species seem to depend mainly on the state of preservation ; in some cases the 

 right valve is almost smooth. Frequently in the larger specimens the later part of 

 the valve is almost without ornament. By far the larger number of specimens 

 which I have seen were obtained from the neighbourhood of Norwich, where 

 it is a characteristic fossil. 



2'v/jj(^— The type of P. concentricus, Woodward, came from the CHialk of 

 Norwich, but cannot now be found. The types of 1'. Maiitclliau.us, d'Orbigny, 

 came from the Senonian of Chavot (Marne). 



JJistrihiition. — M. cor-angainum zone of South Croydon (Haling Pit). 

 /). miinviKitti zone of Clarendon (near Salisbury), of Hartford Bridge and various 

 other localities near Norwich. Upper Chalk of Sussex. 



Peoten (Ciilamys) R()]UNAldinus, iVOrbiijnij, 1847. Plate XXXIV, figs. 7 a,t), 



Qu,h, \)a,h, \{),(,h, 11, 

 \2a—c- Plate XXXV, 

 figs. 1—10. 



18-t-J. PiiCTKN iNTEKSTiuATUS, .1. Leymcrlf. MJm. Sjc. gcol. de Fnmcc, vol. v, 



p. 10, pi. xiii, fiy. 1 (uuu iiiter- 

 stnafus, Miiusttr). 

 1845. — OBLiQUUS, E. Fiirhes. Quart. .Journ. Greol. Soc, vol. i, p. 249 (uou 



obliiiuiis, Sowerby). 

 1847. — KoBiNALDiNUS, A. cVOrhiijiiij. Pal. Fran^. Terr. Cn't., vol. iii, 



p. 587, pi. ccccxxxi, figs. 1—4. 

 ? — — INTEUSTRIATUS, cV O rh I (J 1/1/ . Ibid., p. 51)1, pi. ccccxxxiii, figs. 1 — 5. 



185n. — APTiENsis, A. iVOrU'jiuj. Prodi-, do Pal., vol. ii, p. IIP. 



