UNKNOWN ATLANTIC OR WEST INDIAN I'ORITES. 105 



varying greatly in size from 1 to 2 cm. in diameter. These mounds are separated by only 

 narrow convex valleys, that is without any smooth surface l)etween them. The edges of the 

 stock creep down all round, practically to the substratum, unless prevented by the presence of 

 other organisms. 



The calicles vary slightly from 1*5 mm. downwards. They all tend to bo angular, 

 sharply so in the valleys, less so, that is more subcircular, on the mounds. The wall shows a 

 median line usually broken up into large, smooth, round or angular granules ; when these 

 granules run together, we have portions of a wall-thread. The top edges of the septa have the 

 same character, only they run out into short, very sharp points, directed into the calicle 

 aperture. These tops of the septa are sometimes in a ring of their own, distinct from the wall 

 granules ; sometimes the two are confused according as the wall is thick or thin. The 

 columellar tangle, owing to the thickness of the elements, is somewhat compact and tends to 

 fill up the base of the fossa at different levels. 



The colour of the unbleached stock is an iron-grey. It is very heavy and massive, and 

 built of stout, irregular trabeculse closely packed. 



A comparison of this coral, with the one just described, shows that we are dealing with 

 two distinct corals, and that it is the blindest guesswork to as.sert that they belong to one and 

 the same species. The form here described is not only steeper and has steeper mounds than 

 the one last described, but its elements are strikingly different, as a comparison of the 

 magnified photographs, figs. 7 and 8, PI. VI. will show at a glance. 



a. Zool. Dept. 1906. 1. 1. 13. 



94. Porites West Indies x. 29. (P- Amencana incertce sedis nona et vicesima.) 



[Coll. Duchassaing ; Turin Museum.] 



Syn. Pmites agarkus Duchassaing and Michelotti, Mem. sur les Cor. des Antilles (1860) p. 83. 

 (Neoporites agarkus in the Suppl. (1864) p. 99.) 



Description. — The corallum is like an agaric, explanate, fixed below, but with free edges. 



The calicles are very small, about 1 mm. in diameter. The walls are confusedly, because 

 very openly, reticular. The component threads show slight traces of radial or concentric 

 symmetry ; when the wall is thin, a short zigzag median thread comes to view. Tliese 

 threads vary in thickness, are angular, bent, and run out into fine points, or swell into finely 

 pointed granules. The septa vary greatly in length, slope inwards from the walls, or as 

 separate radial plates, share the angular ragged character of the wall-threads. They are 

 most symmetrically radial when the walls are most regular. The calicles appear shallow. 



This description is based upon the brief remarks made by the original authors and upon 

 a magnified photograph of the calicles of the type specimen in the Turin Museum, kindly 

 supplied for the purpose of this work by Count Peracca (but for technical reasons not 

 reproduced). 



P 



