On the Structure and Relations uf certain Corals. 157 



peculiarities in the structure of the soft parts, and the relations of 

 the tentacles to the septa, described in this paper as occurring 

 in a Stylaster and a Cryptohelia, and the similar facts observed 

 by Sars in the genus AUopora, strengthen the facts brought for- 

 ward by Pourtales, with regard to the coralla, in a very poten- 

 manner. I hope to make a close study of the structure of Sty- 

 laster. The apparent absence of mesenteries is most remarkable, 

 and a similar condition appears to occur also in Milleporn. The 

 number of tentacles and septa in the StylasteridEe seems hardly 

 to follow the usual hexameral law. In the species of Stylaster 

 examined by me there are invariably twenty-two septa and 

 twenty-two tentacles. In Stylaster erubescens, Pourtales describes 

 the septa as being in number from nine to twelve, most frequently 

 eleven. In Allopora miniata the septa are from seven to ten, gene- 

 rally eight. Cryptohelia has commonly sixteen. 



With regard to the affinities of the Milleporidse, no certain con- 

 clusion can be ari'ived at from the few facts yet ascertained. I 

 hope to obtain specimens at Hawaii in sexually mature condition. 



H.M.S. ' Challenger,' North Pacific. 

 21st July, 1875. 



PoSTSCEIPT. 



Since the above was written I have been able to refer at Hono- 

 lulu to Prof. Lacaze-Duthiers's ' Histoire Naturelle du Corail.' I 

 therefore add a few notes. 



In Corallium the contracted polvp presents externally at the 

 surface eight lobes coloured red. When the polyp is expanded, 

 these lobes form a coloured cup with eight dentations at its mar- 

 gin, which surrounds the lower part of the expanded colourless 

 polyp (see pi. 2 of Prof. Lacaze-Duthiers's work). The eight lobes 

 described as closing the mouth of the calicle in the contracted 

 polyp of Heliopora probably occupy a similar position, and have a 

 similar appearance in the expanded condition of the polyp. 



In Corallium the pinnae or barbules of the tentacles are all 

 severally introverted (/. c. p. 57), as well as the tentacles themselves. 

 In Heliopora this appears not to be the case. In the hard tissue 

 of Corallium boring vegetable parasites occur, as observed in Mil- 

 lepora and Pocillop>ora. 



I have further been able to refer to Dana's great work on 

 Corals in the splendid collection of scientific works in the Govern- 

 ment Library at Honolulu, and to other works relating to Helio- 

 pora. 



Dana states (U.S. Expl. Exped. vol. vii. Zoophytes, J. D. Dana, 

 Philad. 1846, p. 539) that the blue colour of Heliopora is of ani- 

 mal origin and is lost on immersion of the coral in nitric acid. 

 The colouring-matter was not analyzed by Mr. Grilliman. 



In the Atlas of the 'Voyage de I'Astrolabe,' Zoophytes, pi. 20. 

 figs. 12, 13, 14, the expanded polyps of Heliopora catrulea are 

 figured by MM. Hombron and Jarquinot. In fig. 14 sixteen very 

 short, simple, conical tentacles are shown, in fig. 13 only fifteen 



