NEWTON: FOSSIL PEAEL-GEOWTHS. 137 



It is quite possible that these specimens were originally derived 

 from the Chalk, because in general appearance and size they agree 

 remarkably well with pearl-growths associated with the genus 

 Inoceramus of Cretaceous rocks. Externally they are straw-coloured, 

 but perfectly white inside ; this, taken in connection with the presence 

 of annelid or molluscan perforations, which were probably made long 

 after their transportation from the Chalk sea, is strongly in favour of 

 their derivative character. 



Mr. F. W. Harmer, F.G.S., has shown me a similar pearly 

 concretion of small size collected in the "Waltonian zone of the Red 

 Crag at Little Oakley, near Dovercourt, Essex, the same deposit 

 having also yielded a fragmentary example of Belemnitella, a character- 

 istic Cephalopod of Upper Cretaceous (Senonian) times. This 

 occurrence would seem further to favour the derivative theory for 

 these interesting spherical bodies. Several papers have been written 

 on the derived fauna of the Crag beds, one of the earliest being by 

 Searles V. "Wood,^ Belemnites being listed as originally coming from 

 the Upper Cretaceous. Pearl-structures, however, from the Crag beds, 

 whether regarded as derived or occurring in situ, do not appear to 

 have been mentioned in connection with the Pliocene fauna. 



Geological age. — Cretaceous (Senonian). Found in the Crag 

 deposits as probably derivative fossils from the Chalk. 



Localities. — Near Orford Castle, and "Waldringfield, Suffolk. 



Collection. — British Museum (Robert Bell and Edward Charles- 

 worth Colls.) [L. 21228 and L. 21229]. 



Pebna oblonga, H. G. Seeley. PI. Y, Fig. 7. 



Perna ohlonga, H. G. Seeley: Ann. Mag. Nat. Hist., 1861, vol. vii, 

 p. 121, pi. vi, fig. 6; H. Woods, Cretaceous Lamellibranchia 

 England, Mon. Pal. Soc, 1905, vol. ii, pt. ii, figs. 19a, b, e, 

 woodcuts on p. 94 ( = reproduction of type figures). 



Professor H. G. Seeley founded this species on some internal casts 

 common to the phosphatic deposits of Cambridge. He noticed that 

 the sides of the valves were frequently furnished with numerous small 

 cavities, proving that the animal must have been a pearl-producer "in 

 prodigious numbers." He further remarked that pearl-like bodies 

 "are often met with detached, sometimes as large as peas: they 

 mostly have a yellowish colour . . . but, besides the free pearls, 

 pearls attached to the shell were far from uncommon, and in some 

 individuals so numerous as to remind one more of artificial productions 

 in the Chinese Anodon than of a natural growth. No nacreous 

 specimens have been found which can satisfactorily be considered as 

 attached pearls ; but their impressions, left on phosphatic casts, are 

 unmistakable." 



' Wood, Searles Y., " On the Extraneous Fossils of the Eed Crag" : Quart. Journ. 

 Geol. Soc, 1859, vol. xv, p. 38. 



VOL. VIII. — OCTOBER, 1908. 12 



