192 Roy at Society. 



It has hitherto been a matter of regret that the Hj'-droidea were 

 of such a structure as to be unsuitable * for preservation in the 

 fossU state, and that thus we were almost, excepting as far as 

 GraptoHtes are concerned, without direct evidence as to the forms 

 which may have been presented b}'^ their remote ancestry- We 

 have now two families excellently adapted for preservation as 

 fossils, viz, the Milleporidae and the Stylasterid®. At present no 

 members of these families appear to have been observed in rocks 

 older than the tertiary deposits. A single species only, Distichopora 

 antiqua, is known to occur in tertiary beds in France, at Chaumont 

 and Valmondois t ; but now that special attention wiU be directed 

 to these corals, and their structure is better understood, no doubt 

 allied fossil forms will be detected. It seems just possible that 

 amongst Palaeozoic corals such forms as Cyathonaxia may have 

 been tenanted by a group of hydroid zooids with a large alimen- 

 tary zooid situate upon the projecting style. Cystiphyllum vesi- 

 culosum has a crowd of small slit-like pits covering the inner sur- 

 face of its calicle, which have all the appearance of having been 

 tenanted by hydroid tentacular zooids. I cannot, however, now 

 refer to specimens ; indeed I have never seen any. Ampullae seem 

 to be absent in these corals ; but in shallow-water forms, as in 

 Millepora, they probably would be so. It is quite possible that 

 the Millepores produce Medusae. 



Although the Milleporidae take a very large part in the forma- 

 tion of coral reefs, the Stylasteridae have very little share in the 

 building up of these structures, being for the most part confined 

 to the deep sea. A few species only occur in shallow water, and 

 apparently not in great abundance. In deeper water, however, 

 the Stylasteridoe are most luxuriant. Immense quantities of a 

 large flabellate red Distichopora, brought from the Marquesas group, 

 are sold to tourists at Honolulu. The corals are said to come 

 from deep water. The results of the ' Challenger's ' dredging off 

 the Eio de la Plata in 600 fathoms showed that at that depth 

 very considerable deposits of calcareous matter must be formed by 

 these various genera of hydroid corals, growing associated as they 

 do in masses and attached to one another. Large dead masses of 

 Polypora brought up by the dredge were especially remarkable, 

 weighing more than 1 lb., and forming bases of attachment for 

 sponges and all kinds of other animals. 



I am at present engaged in preparing a series of drawings illus- 

 trative of the anatomy of the Stylasteridae, which I hope shortly 

 to lay before the Eoyal Society, together with a more complete ac- 

 count of the structure of these corals. 



South Atlantic, 

 March 24, 1876. 



* Allman, /. c. vol. ii. p. 231. 



t MM. Milne-Edwards & Haime, I. c. t. iii., Appendice, p. 451, 



