. Catalogue of the madreporarian corals in the British Museum (Natural History). Scleractinia. ANALYSIS AND DISTRIBUTION OF TYPES OF CALICLES. 273 hence we ought to find extraordinary variation in this respect. That, however, is not the case. The rule is that the composition of the wall is very uniform. We find, for instance, that while in valleys and depressions where the caUcles are squeezed together the trabeculse of the calicular skeleton may be almost indefinitely aborted, on convexities where the calicles have abundance of room it is seldom that more than one extra trabecula appears. If
. Catalogue of the madreporarian corals in the British Museum (Natural History). Scleractinia. ANALYSIS AND DISTRIBUTION OF TYPES OF CALICLES. 273 hence we ought to find extraordinary variation in this respect. That, however, is not the case. The rule is that the composition of the wall is very uniform. We find, for instance, that while in valleys and depressions where the caUcles are squeezed together the trabeculse of the calicular skeleton may be almost indefinitely aborted, on convexities where the calicles have abundance of room it is seldom that more than one extra trabecula appears. If the convexity rises very rapidly the trabeculae may all disappear as such, and the skeleton becomes a streaming lamellate C D Fig. 4.—Diagrams illustrating the structure of the theca of Pontes. A, an ideal vertical section through a simple walled calicle of a colony ; w, the wall trabecula ; $(j, the septal granule ; "p, the palus; d, the central tubercle (these three are seen, like w, to be the tips of trabeculas). B, a horizontal section of a calicle in a colony in which the thecse are slightly separated so that the syiiapticulaj joining the wall trabecula; (w^) with those of adjacent calicles {iir) have a zigzag course. C, a vertical section through a compound wall, which appears when the simple walls (w) are far enough apart to admit of an inter- vening trabecula, in this case figured as rising above the walls (w) as a wall-ridge (lir), making w look like another gran vile of the septal edge (the " wall granule"). D, an ideal parent calicle to explain the origin of intervening trabecula3; they are homologous with costal trabecular ((;), one or more of which are able to appear if the calicles in a colony are far enough apart to admit them ; ef, epithecal saucer or prototheca. We have, then, nothing to do but to go forward and endeavour to arrange those phenomena in the Porites calicle which alone seem to admit of tabulation, and those are the varia
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