522 PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION

is a modification of tlie condition seen in fig. 79, only the radiating partitions are muchmore numerous, and consequently the compartments are very much smaller. Butexternally 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 opaqueradiating 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 theyenclose having been hollow, are again filled by calcic carbonate, hence the greatertranslucency of this outer sphere-layer as compared with the inner one.

Fig. 69, Calcisphcera hexagonatci .—This form is not very uncommon, though moreso than the variety last described. The central cavity is again filled with crystallinecalcic carbonate, and the dark, double-inner sphere-wall is now more clearly definedthan 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. Itsdistinctive feature is seen in the outline of the outermost investing layer. So far asstructure is concerned it differs in no respect from the same layer in fig. 67—save thatit is somewhat thicker—but it has a perfectly hexagonal peripheral outline, the sidesof the hexagon being almost geometrically equal in size; occasionally they exhibit aslight degree of convexity. The specimen figured is rather larger than fig. 67, havinga diameter of about ’0066.

Fig. 68, Calcisphcera Sol .—This form exhibits a general resemblance to fig. 67, onlyboth 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 distinctivefeature, however, is found in the outermost sphere-wall, which is prolonged intonumerous elongated pointed radii, arranged with a considerable degree of regularityboth as regards size and position. These radii are somewhat translucent, like theinvesting layer of which -they appear to be extensions. I think it would not bedifficult, by persevering search, to find specimens linking this form to that of fig. 6 7.

Figs. 71 to 77 appear to represent a series of modifications of fig. 70, inasmuch asin them the sphere-wall appears to be single and homogeneous, but much thinner thanin that example, and the surface is drawn out into a series of tubercules and spines ofvery variable number, length, and acuteness. In many, the section of the sphere isrounded, as in fig. 71. In others it is pentagonal as in figs. 72 and 73, whilst in 76it becomes trigonal. But I find so many connecting links between these varieties thatI propose to unite all this series under the name of Calcisphcera spinosci. So far as Ican discover, the entire series differs from figs. 67, 68, and 69, in the simpler structureof the sphere-wall.

Fig. 78 is a representation of an example in which, as also in fig. 75, the section hasonly cut off a small tangential slice from one side of the sphere, the remainder of thehemisphere being seen through the somewhat translucent matrix in which it isembedded. It is larger than the other specimens figured, the diameter of its sphere-