94 MADREPORARIA. 



The figures of the calicles are taken from the top of one of the upright processes, and 

 show the more or less open axial reticulum at the tip. The basal calicles are a little more 

 regular, and when looked at not too closely, show the same granular or bristly appearance 

 described for specimen a. This featui-e is so rare that we have to assume that the two are of 

 the same kind, and owe their differences to the effect of accidental conditions. On the other 

 hand this common feature may be in adaptation to some factor of their common environment 

 — a bristly surface might be protective against the attachment of Balanid larvae, swept with 

 others through the Gorgonid skeleton. 



h. On a Gorgonid skeleton. Zool. Dept. 43. 3. 6. 98 (part) 



82. Porites West Indies x. 17. (P. Americana incertce sedis septimadecima.) 

 (PI. V. fig. 6 ; PI. XVI. fig. 3.) 



[West Indies, coll. Bowerbank ; British Museum.] 



Description. — The corallum rises into tall, thin, branching stems, nearly uniform in thick- 

 ness (1 • 5 to 2 cm.), the whole way up. The forking, which takes place at irregular distances, 

 from 2 to 3 cm. apart, seems mostly to result in one prong either forming a lateral spur, long 

 and tapering, or short and mammillate, or even aborting altogether as a knee-like protrusion 

 while the other thickens, carries on the stem, and again forks. The living layer is about 

 5 cm. deep. 



The calicles are ill-defined, superficial, and yet fairly conspicuous ; they are mostly small, 

 but vary in size from 1 • 5 to • 75 mm. The wall is very irregular and seems to consist 

 of continuous, smooth, chalky -looking flakes with very crisp edges, varied in width, here wide 

 there narrowed to a thread. Processes grow out of these flakes and swell into highly echinu- 

 late or frosted knobs ; the vertical processes raise the, wall ; the lateral processes form the septa, 

 the swellings of the latter form the septal granules. The septa are very irregular, sometimes 

 broad and flaky, sometimes thin, always with crisp echinulate sides. The pali are also irregular, 

 either as granules or as flat, crisp-edged, horizontal plates ; these, like the septa, fuse together 

 quite irregularly, and consequently obscure the radial symmetry. The central fossa, which is 

 large, is mostly shallow and with a small central tubercle. The interseptal loculi are of all 

 shapes and sizes, one or two usually very large and conspicuous. The tips of the terminals 

 are rounded masses of open reticulum apparently of stout threads which are the edges of 

 streaming lamellae. 



The section shows the axial strand not very pronounced, and the cortical layer gradually 

 changing in the direction of considerable development of the concentric elements. 



There are two specimens from the Bowerbank collection, unfortunately without any 

 recorded locality. There can, however, be little doubt that they are West Indian forms. 

 They are tall and slender, and might thus be easily recognised again from their growth-forms. 

 For an extreme development of this modification, in which one prong carries up tlie stem and 

 the other aborts as a spiir, see P. Barbados 6, p. 38. The calicle skeletons, in being lamellate, 

 are rare in branching forms ; cf., however, Poi'ites Florida 1, p. 71. 



«, h. Zool. Dept. 77. 5. 21. 207 and 208. 



