W. J. Sollas — Green Grains in the Cambridge Greensand, 541 



This membrane may be composed of sulphate of lime, which has 

 impregnated the calcareous skeleton of the coccolith after its death, 

 though I doubt this. 



The form we have just described is evidently a flat or somewhat 

 concave disc, thickened at its edges into a ring-like border, and at 

 its centre into a granulated area with one of the granules much 

 larger than the rest. It is well enough preserved in the glauconitio 

 granules to show clearly the outer annulus and the central granule. 

 Figs. 6 and 6 a. represent a very common modification of this 

 form, which appears to me to result from a circumferential constric- 

 tion round the edge, grooving it, so as to produce a resemblance to a 

 pulley-wheel. It has not been observed within the green grains. 

 Fig. 7 is a large form of Fig. 5, which attains relatively to the latter 

 form a size fully double that which is shown here. The outer ring 

 much thickened appears to be marked along the middle of its upper 

 margin by a rounded ridge, which on focussing down resolves itself 

 into a number of granules, somewhat irregularly arranged. Broken 

 pieces of this variety are to be seen in the green grains. 



The next form, Fig. 8, is similar to Fig. 5, but differs from it by 

 the presence of a transverse bar produced from the annulus, along 

 the minor axis of the ellipse, and which divides the central oval 

 area into two parts, each with its cloudy centre and refractile granule. 

 To all appearance this is simply Fig. 5 undergoing fission, and yet 

 the whole structure consists of carbonate of lime. In connexion 

 with this, it is noticeable that while both of these coccoliths vary in 

 . size, yet that of Fig. 5 does so to a much greater extent than that 

 of Fig. 8. 



In the next variety. Fig. 9, the process of sub-division has gone 

 a step further, and the space within the ring is partitioned off into 

 four by a thickening of the disc along two axes at right angles to 

 each other. 



The next division of the coccolith is into eight, as shown in 

 Fig. 10, and so far each step in the process has followed the geo- 

 metric progression, 1, 2, 4, 8 ; in Fig. 13, however, we have an 

 exception to this rule, since it exhibits nine sub-divisions within its 

 inclosing annulus, and we omitted in passing to notice another very 

 rare form where the loculi number three. Fragments of the forms 

 Figs. 10 and 13 are found in the Chalk-marl (Fig. 11) looking like a 

 residue left on the dehiscence of the other part of the coccolith ; such 

 a fragment (Fig. 14) is the only instance of these last complicated 

 forms which I have observed in the green granules, and it appears 

 to have been derived from an even still more complex type, since 

 if the missing part be supplied, the restored ring would present, I 

 should judge, nearer 16 than 8 loculi. All the forms from Fig. 5 to 

 13 vary in the relative length of their major and minor axes, and 

 sometimes become quite circular; Fig. 12 represents the round 

 variety of Fig. 10. 



All again may develope stalks or stems at right angles to the plane 

 of the disc, e.g. Fig. 15, which is derived from a form like Fig. 5 ; 

 Fig. ,17 a, from Fig. 17 ; and Fig. 18 from Fig. 6. In forms like Figs. 



