26 MADREPORAEIA. 



horizontally into flakes, the edges of which seem to be run out along the septa. The latter 

 are prominent, crooked, nodulated or angular, and fuse into the tjrpical four pairs and 

 ventral triplet. The pali are but feebly developed as slight swellings at the points of fusion. 

 A small columellar tubercle is here and there seen, but no tangle is visible ; the fossa is 

 consequently deep and open, as are also the interseptal loculi. The skeleton consequently 

 appears to have a loose, open texture. 



The locality of this Poritcs (No. 197 bis a in the Paris Museum), far from any known 

 coral reef, and its flattened under surface suggesting that it rested on some soft, perhaps 

 muddy, bottom, are not the only interesting points about it. We have to note its thread-like 

 walls and feeble pali as indicative of the greater development of the horizontal than of the 

 trabecular elements. This character helps to unite it with the other Atlantic and West Indian 

 forms as against the Indo-Pacific, including the specimen from the Cape of Good Hope with its 

 tall, thin, trabecular walls. 



There are in all three specimens ; the above description is based upon the one with the 

 smallest calicles ; the two others were obscured by animal matter, which made it difiicult to 

 examine the details. 



2. Porites Cape Verde Islands 1. (P. Insularum Arsinarii prima.) 

 (PI. I. fig. 2 ; PI. XVII. fig. 1.) 



[St. Vincent, coll. H.M.S. ' Challenger ' ; British Museum.] 



Syn. Porites Gvadalupensis, Quelch (non Duchassaing and Michelotti), Chall. Rep. xvi. (1886) p. 181. 



Description. — The corallum is thick, encrusting, and with a tendency to throw out 

 laterally rounded lobes like the blunt pseudopodia of a great amoeba. 



The calicles are about 1 • 25 mm. in diameter (but of very different sizes), deep, mostly 

 rounded, but here and there drawn out of shape. The walls stand up steeply, built of very 

 irregular tralieculae, here thin, branching and ragged, there membranous. Their top edges are 

 filamentous, either as a very slight or else as a very pronounced zigzag ; in the latter case, 

 the wall looks thick. The septa begin as short thin filaments projecting from the angles 

 of the zigzag ; they lengthen very gradually and meet in a tangle, which, deep down, forms an 

 irregular floor to the fossa without any conspicuous traces of the typical septal arrangement ; 

 slight traces here and there of pali may be seen, but the typical formulae are nowhere 

 completed. 



In vertical section the irregularity of the trabeculije is the most conspicuous feature ; 

 thick and nodulated, deep down, they thin away near the surface into an irregular network 

 in which they cease to be conspicuous elements. 



The colour seems to have been a dark ochre. 



Mr. Quelch described this coral as closely allied to the massive Red Sea forms " arenosa " 

 and " conglomerata " ! But in this form, though trabeculae carry up the walls to a considerable 



