DISTRIBUTION OF TYPES OF CALICLE. 



139 



( = the coenenchymatous forms or Synarcea of authors), are not yet known among the West 

 Indian Pontes. They indicate, as already explained in Vol. V. p. 15, looser colonies, that is, 

 stocks in which the calicles are wide enough apart to allow costal elements to appear. 

 Wliether the absence of these can be correlated in any way with the other difference pointed 

 out between the Pontes of the two regions, remains to be seen. 



Fig. 1. — Diagrams illustrating the structure of the theca of Porites. A, an ideal vertical 

 section through a simple walled calicle of a colony ; w, the wall trabecula ; sg, the septal 

 granule ; p, the palus ; d, the central tubercle (these three are seen, like w, to be the 

 tips of trabeculee). B, a horizontal section of a calicle in a colony in which the thecae are 

 slightly separated so that the synapticulae joining the wall trabeculse («>') with those of 

 adjacent calicles (w^) have a zigzag course. C, a vertical section through a compoutid 

 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 (wr), 

 making w look like another granule of the septal edge (the " wall granule "). D, an 

 ideal parent calicle to explain the origin of intervening trabeculie ; they are homologous 

 with costal trabeculse (c), one or more of which are able to appear if the calicles in a 

 colony are far enough apart to admit them ; ep, epithecal saucer or prototheca. 



A. Forms whose calicles have traces of more than three rings of trabeculae. 



P. Cape Verde Islands 2 (PI. II. fig. 3). Among the thicker walls some appear to 

 have more than three rings. 



P. Bahamas 1 (PL IV. figs. 2, 3, 4, 5, 6). The walls here vary much in thickness, 

 and it is only in the thicker parts that the extra trabeculae can be assumed, for 

 the tendency to become purely reticular obscures the actual details. 



P. West Indies x. 15 (PI. V. fig. 3). The walls are here thickened throughout; 

 the calicles are unique among the West Indian forms, in that the trabeculse as 

 seen at the surface are graduated in thickness from the pali which are normal 

 outwards on to the wall where they are thick, though see P. Cwpe Verde 

 Islands 2 above. The variation in the thickness of the walls is very great. 



T 2 



