898 MISS R. M. HARRISOX AND MISS M. POOLE ON [Dec. 14, 



we are really dealing, not with several, but with a single species 

 which is highly variable. 



Genus Heterocyathus Milne-Edwards &, Haime. 



Heterocyathus ^quicostatus Milne-Edwards & Haime [24]. 

 (Plate LXXXY. figs. 1 a-lf.) 



Stephanoseris rousseaici Milne-Edwards & Haime [27]. 



H. philippi'nensis Semper [34]. 



H.2>arasiticus Semper [34]. 



H. 2)ulchellus Rehbei-g. 



H. ohlongatas Rehberg. 



H. cequicostahcs Gardiner [16]. 



The above list of synonyms of H. ceqnicostatas is due to 

 Gardiner [16], with the exception of Stephanoseris rousseaui 

 which was subsequently added by Bourne [5]. 



The specimens fall into three main types, of which two are 

 identical with those described and figured by Gardiner [16] ; 

 while the third is rather markedly difterent and resembles more 

 closely the figure given by Semper of his now abolished species 

 H. philippinensis. The accompanying photographs (PL LXXXV. 

 figs. 1 cc-f), however, show that this type is connected with the 

 second type of Gardiner by beautifully intermediate forms. 



All the specimens are free with smooth bases, and have the 

 apertui-e of the Aspidosiphon chamber well at one side and often 

 on a slight protuberance. 



Type I. 49 specimens. The corallum is peai'-shaped, 

 14'5 X 10"5 mm. and 6 mm. in height. Lateral pores are confined 

 to the basal surface. The costae are equal in number to the septa, 

 very clearly defined and extending well round on to the basal 

 surface. They are closely covered with small granules. The 

 septa form four cycles of six systems ; the primaries and second- 

 aries are the largest and equal in size, the quaternaries come next 

 in size, the tertiaries being the smallest. Crenulated pali stand 

 before all the septa except those of the third cycle, and are 

 indistinguishable from the inner edges of the septa on one hand 

 and from the columellar trabeculfe on the other. Both pali, 

 trabecular and septa are covered with spiniform granules. The 

 calicular fossa is hardly 1 mm. in depth, and 2x3 mm. in dia- 

 meter owing to the crowded pali. 



Type II. 22 specimens. The corallum is pear-shaped or round, 

 of the same size as type I., but generally slightly taller, 8 mm. 

 The lateral pores are distributed in an irregular manner round 

 the lower part of the wall of the coi-allum and not restricted to 

 the base as in type I. Costas as in type I., but tending to be less 

 regular in size. The septa are in four cycles of six systems, but 

 here the primaries are clearly marked off from the secondaries 

 by their greater prominence and larger size, and foi-m, together 

 with their adjacent quaternaries, a well-defined six-rayed star, 

 alternating with the points of which the secondaries with their 



