17 



MR. JUKES-BROWKE AND PROF. HARRISON 



usually by an elongate nuclear spot (fig. 8). Around the disc is a 

 broad marginal rim, in width nearly one third that of the organism, 

 made up of concentric rings. This rim is ornamented in the larger 

 coccoliths by radiating striae, or ribs, and occasionally around the 

 centre of the rim are minute bead-like elevations (see fig. 7). 

 The smallest (fig. 9) have a more circular outline, and have only a 

 central spot and a rim without ornamentatioD. The largest oval 

 form measured was '023 mm. in its longest diameter. 



The stellate bodies (figs. 1-6) consist of rays whi«h emanate from 

 a common centre, in number from five (rarely three) to sixteen, 

 and between these extremes every variation occurs, the most 

 common forms being those of eight to twelve rays. In those which 



4% m M^ M 





f>o> 



Explanation. 

 I from the chalky Oceanic Deposits of Barbados. 

 Fig. 5 illustrates the appearance of (4) and (6) when viewed edgeways. 



Figs. 1-6. Crystalloids 

 Figs. 7, 8, 9. Coccolilhs 



have the smallest number the rays are shaped like elongated 

 parallelograms (fig. 1) arranged on a common base ; they occa- 

 sionally bifurcate at their summits (fig. 2). This latter peculiarity 

 is rare in the calcareous earths, but occurs commonly in the fora- 

 miniferal muds to be hereafter noticed. 



With the increase in number the ray becomes more acutely 

 pointed and the interval between each is filled up : the result is a 

 rosette-like disc, with serrated outline and radiate ornamentation 

 corresponding to the number of the rays (figs. 4 and 6). The centre 

 has then on one side a nuclear spot, not seen in those with few rays, 

 and on the other the centre is produced to a kind of stalk, in length 

 about half the diameter of the disc (see fig. 5), the whole when 

 seen edgeways reminding one of a short or broken tintack ; the 

 ornamentation of the disc appears to be carried towards the summit 

 of the stalk as ribs or fiutings. The largest of these measured 

 •015 mm. in diameter. These stellate bodies are exceedingly 

 abundant in the calcareous Oceanic Deposits of Barbados, and play 

 almost as important a part in the formation of those deposits 

 as the often-described coccolith. 



Although one variety with six rays (fig. 2) certainly occurs in the 

 Atlantic ooze and one very similar in the muds from West Java, 

 they do not appear to have attracted special attention. Dr. Sorby, 



