746 MR. J. STANLEY GAEDiNEB, oif [June 6, 



Hydnophora exesa, H. demidojffi, and H. polygonata, Milne- 

 Edwards & Haime, Cor. ii. pp. 420-422 (1857) (which see for 

 other earlier references). 



Milne-Edwards and Hairae stated their opinion that the three 

 species above mentioned would be found to be diflFerent stages of 

 growth of one species. My specimen, on which I venture to 

 propose the absorption of H. demidovii and H. polygonata, is a 

 colony 13 by 11 cm. across and 8 cm. high. The underpart is 

 dead, but the upper parts have sent out over it a thin growing 

 edge, free in places for 2-3 cm. The upper surface is a mass of 

 low anastomosing branches and lobes, varying from 7 mm. to 

 2*5 cm. in diameter, of nearly all the same height, dead in three 

 places, where they had apparently reached the surface and become 

 exposed to the sun at low tide. 



The thin growing-edge is very fine, and its monticules have the 

 general character of those given by Milne-Edwards and Haime 

 for H. exesa, save only that, owing to the irregular surface over 

 which the edge is growing, the valleys are seldom more than 4 mm. 

 broad. The under surface is similar to that described for H. demi- 

 dqffi, but the epitheca is in many places thick and well-marked. 

 The length of the monticules on the lobes varies from 2 to 7 mm., 

 being commonly greater on the larger and more central lobes. 

 The monticules vary up to 6 mm. from one another, and up to 

 7 mm. in height. 



Large and small septa alternate one with another, the large 

 alone fusing in the centre of the valleys. The septa are not so 

 thick, and are nearer to one another than in //. lohata ; their edges, 

 too, are rougher, and have no conspicuous teeth as in that species. 

 The calicinal centres are not recognizable on the lobes, but on the 

 thin growing-edge are fairly distinct. (PI. XLVIII. fig. 3.) 



Eunafuti ; outer reef. 



Quek'h distinguished a species, H. tendla, in his ' Challenger ' 

 Report, from H, exesa and H. demidoffi mainly by its mode of 

 growth. I have already pointed out the great differences between 

 the Wakayan reef-specimens of H. microcona and the Funafuti 

 lagoon-specimens, and it seems to me to be probable that this is a 

 case of a new species having been described when simply different 

 conditions prevailed, causing different rates of growth. Whether ' 

 the specimen above referred to H. exesa is really that species or 

 H. polygonata, there seems to be no doubt but that H. tenella is 

 only a synonym of H. exesa. 



G-enus GoisriASTR^A. 



Goniastrma^ Milne-Edwards & Haime, Corapt. rend, de I'Acad. 

 des Sc. xxvii. p. 495 (1849), and Cor. ii. p. 444 (1857). 



This genus is easily distinguishable from Astrcea by the possession 

 of distinct pali. These are joined at first to the septal edges by 

 trabeculse, but later the connection becomes a distinct plate, so 

 that they appear in section like thickenings of the septal edges. 



