522 PROFESSOR W. C. WILLIAMSON -ON THE ORGANIZATION 
is a modification of the condition seen in fig. 79, only the radiating partitions are much 
more numerous, and consequently the compartments are very much smaller. But 
externally to this sphere-wall we now have a second investing layer, which is semi- 
translucent by transmitted light, and in which the existence of numerous opaque 
radiating lines is sufficiently obvious. I presume that this is a second sphere-wall, 
constructed like the inner one, but that, in it, the primary calcareous radiating parti¬ 
tions have been extremely thin, whilst the larger, long, narrow cavities which they 
enclose having been hollow, are again filled by calcic carbonate, hence the greater 
translucency of this outer sphere-layer as compared with the inner one. 
Fig. 69, Calcisphcera liexagonata .—This form is not very uncommon, though more 
so than the variety last described. The central cavity is again filled with crystalline 
calcic carbonate, and the dark, double-inner sphere-wall is now more clearly defined 
than in fig. 67. The space between the two layers of which this sphere-wall consists, 
is again occupied by radiating opaque partitions separated by translucent lines. Its 
distinctive feature is seen in the outline of the outermost investing layer. So far as 
structure is concerned it differs in no respect from the same layer in fig. 67—save that 
it is somewhat thicker—but it has a perfectly hexagonal peripheral outline, the sides 
of the hexagon being almost geometrically equal in size; occasionally they exhibit a 
slight degree of convexity. The specimen figured is rather larger than fig. 67, having 
a diameter of about *0066. 
Fig. 68, Calcisphcera Sol .—This form exhibits a general resemblance to fig. 67, only 
both its opaque, inner sphere-wall, and its outer translucent layer are thinner in pro¬ 
portion to the entire diameter of the organism than in that species. Its distinctive 
feature, however, is found in the outermost sphere-wall, which is prolonged into 
numerous elongated pointed radii, arranged with a considerable degree of regularity 
both as regards size and position. These radii are somewhat translucent, like the 
investing layer of which they appear to be extensions. I think it would not be 
difficult, by persevering search, to find specimens linking this form to that of fig. 67. 
Figs. 71 to 77 appear to represent a series of modifications of fig. 70, inasmuch as 
in them the sphere-wall appears to be single and homogeneous, but much thinner than 
in that example, and the surface is drawn out into a series of tubercules and spines of 
very variable number, length, and acuteness. In many, the section of the sphere is 
rounded, as in fig. 71. In others it is pentagonal as in figs. 72 and 73, whilst in 76 
it becomes trigonal. But I find so many connecting links between these varieties that 
I propose to unite all this series under the name of Calcisphcera spinosa. So far as I 
can discover, the entire series differs from figs. 67, 68, and 69, in the simpler structure 
of the sphere-wall. 
Fig. 78 is a representation of an example in which, as also in fig. 75, the section has 
only cut off a small tangential slice from one side of the sphere, the remainder of the 
hemisphere being seen through the somewhat translucent matrix in which it is 
embedded. It is larger than the other specimens figured, the diameter of its sphere- 
