46 MADREPOEAEIA. 



This is one of the encrusting group usually called collectively P. astrceoides and regarded 

 as a single species. See remarks upon this group in the Introduction, p. 15, and Table III. 



Through the kindness of Count Peracca we can gather some further details of calicle 

 structure of this specimen from the two magnifications shown on PI. II. figs. 2 and 3, which 

 show two extreme types of calicles, found on Duchassaing's type specimen, which is preserved 

 in the Turin Museum. While the walls shown in fig. 2 are those generally regarded as typical 

 of "P. astrceoides" and occur very frequently, here and there the walls proliferate into a thick, 

 jagged, flaky network. There are reasons for believing that this alteration may be due to the 

 somewhat inconvenient juxtaposition of other organisms. We certainly learn from the 

 specimens of P. Bahamas 1, that this kind of wall-proliferation may be so produced. See 

 PI. IV. figs. 3 and 4, which are alterations of fig. 2 due to such interference. 



Duchassaing's name for this coral was given by Quelch in the ' Challenger ' report to an 

 encrusting form from Cape Verde Islands, see p. 26. 



27. Porites Antigua 1. (P. Antigum prima.) (PI. II. fig. 4; PI. X. fig. 1.) 

 [Packam Sound Eeef, coll. Gregory ; British Museum.] 



Description. — The corallum rises on a central stem and divides dichotomously to form a com- 

 pact cluster of very short stems about 1 ■ 5 cm. thick, and forking about every 1 • 5 cm. apart ; 

 the terminals are short, thick, rounded knobs. The living layer is at least 3 cm. deep. 



The calicles are 1 • 5 mm. in diameter, shallow and open, but with a low, sharply raised 

 wall, which makes them look polygonal. The walls show a thin, smooth, zigzag thread some- 

 what obscured by the diverging septa which branch off each side ; as the skeleton thickens, 

 they are completely lost; seen sideways they appear here and there ragged and somewhat 

 lamellate. The smooth septa seem to swell rapidly into frosted or echinulate knobs ; as they 

 project from the wall they are all of different lengths, one or two perhaps uniting with their 

 corresponding pali high up, the others only lower down, though their pali may rise up freely 

 above them. The pali and the septal knobs show signs of expanding laterally into horizontal 

 flakes a short way down, and incipient fringes appear round them. But in spite of this the 

 reticulum of the intracalicular skeleton remains open enough to see deep down into the depths. 

 The pali (5) rise from a long, scattered, columeUar tangle not very sharply circumscribed by 

 the ring of interseptal locnli, which are all irregular in outline and arrangement. 



The section shows a rather open network with conspicuous radiating trabeculse and well- 

 developed concentric elements. 



The specimen shows a regular growth which had forked four or five times, and had 

 attained a height of some 8 cm. when it was overturned, and a new growth had spread over 

 one side, and from it mammillate processes, some 1 " 5 cm. high, had arisen. We have then to 

 gather the real characters of this Porites from the dead overturned stock. And this requires 

 some care, because some of its tips had evidently survived the overthrow, and continued to 



