136 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



lateral prolongations. Length of pearl-growth, 36 ram. ; diameter of 

 spherical part, 14 mm. 



Geological age. — Cretaceous (Senonian). 



Locality. — Charlton, Kent. 



Collection. — British Museum (Rev. Norman Glass Coll.) [44676]. 



Inoceramus. pi. Y, Figs. 4-6. 



Inoceramus, J. Morris : Ann. Mag. 'Nat. Hist., 1851, vol. viii, p. 89, 

 pi. iv, figs. 13, 14. 



Morris's section (his fig. 14) represents another pearl concretion of 

 considerable size, its diameter measuring 20 mm., this measurement 

 being obtained from the illustration, as its presence among British 

 Museum specimens has not been satisfactorily determined. It is 

 stated to be an unattached form, of which there are two or three 

 other examples, although much smaller than exhibited by the 'Morris' 

 section. One of these appears to be the original of fig. 13 of the 

 ' Morris ' plate, which exhibits an exactly similar radio-concentric 

 structure to the attached form previously mentioned, and from its 

 lithological resemblance would doubtless have originally belonged to 

 an Inoceramus shell, being so regarded by John Morris. Under a strong 

 lens the external surfaces of the concentric layers are observed to be of 

 minute prismatic structure. 



A magnificent section of a further example, figured on PI. V, 

 Figs. 4, 5, of this paper, from the same locality as those represented 

 by figs. 13 and 14 of the 'Morris' plate, has been most kindly placed 

 at my disposal for reference in this paper by its possessor, Mr. B. B. 

 Woodward, F.L.S. It has a diameter of 1 1 mm., and not only 

 shows the normal structure of the exquisitely fine and straight 

 radial striations crossed by the periodical concentric lines, but the 

 nucleus under a ^ inch objective appears to be of cellular or prismatic 

 structure. It seems probable that this cellular character of the 

 nucleus may represent the encysted larval condition of Cestode or 

 other parasitical worms, such as has been figured by Messrs. Herdman 

 and Hornell in connection with modern pearl structures ("Pearl 

 Production " : Report to the Government of Ceylon, etc., 1906, 

 pt V, pi. i, fig. 14). 



Geological age. — Cretaceous (Senonian). 



Locality. — Northfleet, Kent. 



Collection. — British Museum (N. T. Wetherell Coll.), and collection 

 of B. B. Woodward, Esq. 



Inoceramus. 



The British Museum collection also contains some isolated examples 

 of spherical pearl bodies, which occur in the Crag deposits of Suffolk 

 (Orford Castle district and Waldringfield), and which vary from 3 to 

 10 mm. in diameter. Sections exhibit the usual concentricity of 

 formation, as well as the radial structure as seen in specimens from 

 valves of Inoceramus. Externally the growth layers can be seen by 

 their fractured edges, and sometimes the surface is pierced by minute 

 and larger perforations, the work of a boring organism of some kind. 



