1875.] Structure and Relations of certain Corals, 69 



dopora, and Errina. The 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 Allopora, strengthen the facts brought 

 forward by Pourtales, with regard to the coralla, in a very potent man- 

 ner. I hope to make a close study of the structure of Stylaster. The 

 apparent absence of mesenteries is most remarkable, and a similar con- 

 dition appears to occur also in Millepora. The number of tentacles 

 and septa in the Stylasteridse 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, generally eight. Cryptohelia has commonly sixteen. 



With regard to the affinities of the Milleporidae, no certain conclusion 

 can be arrived 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. 



Postscript. 



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

 Prof. Lacaze-Duthiers's ' Histoire Naturelle du Corail.' I therefore add 

 a few notes. 



In Corallium the contracted polyp 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 margin, 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 pinnse or barbules of the tentacles are all severally 

 introverted (I. 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 Millepora and Pocillopora. 



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

 the splendid collection of scientific works in the Government Library at 

 Honolulu, and to other works relating to Heliopora. 



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

 1846, p. 539) that the blue colour of Heliopora is of animal origin and 



appears indistinguishable from the genus Cryptohelia of the same authors. Endohelia 

 is founded on a Japanese species. The 'Challenger' dredged a coral certainly not dis- 

 tinguishable from Cryptohelia generically off the coast of Japan. 



