140 MANUAL OF ZOOLOGY. 



careous. It is the most familiar member of the family, and is 

 largely imported for ornamental purposes. Red coral consists 

 of a branched, densely calcareous sclerobasis, which is finely 

 grooved upon its surface, and is of a bright-red colour. The 

 corallum is invested by a ccenosarc, also of a red colour, 

 which is studded by the apertures for the polypes, which are 

 white, and possess eight pinnately-fringed tentacles. The 

 entire ccenosarc is channelled out by a number of anastomos- 

 ing canals, which communicate with the somatic cavities of the 

 polypes, and are said to be in direct communication with the 

 external medium by means of numerous perforations in their 

 walls. The entire canal system is filled with a nutrient fluid, 

 containing corpuscles, and known as the " milk." 



CHAPTER XV. 



RUGOSA. 



ORDER III. RUGOSA. Until quite recently all the members 

 of the Rugosa were believed to be extinct, and with the excep- 

 tion of Holocystis elegans of the Lower Cretaceous rocks, it was 

 believed that no example of the order had survived the close 

 of the Palaeozoic period. Some Tertiary forms have, however, 

 been now discovered ; whilst the recent Guynia of the Medi- 

 terranean, and Haplophyllia of Florida, are Rugose corals. 

 With the soft parts of the Rugosa we are, of course, almost 

 entirely unacquainted, and the definition of the order must 

 therefore be founded upon the characters of the corallum. The 

 corallum-in the Rugosa is highly developed, sclerodermic, with 

 true thecse, and often presenting both septa and tabulae com- 

 bined. The septa are in multiples of four (fig. 43, B), unlike 

 the recent sclerodermic coralla, in which they are in multiples 

 of five or six. There is, further, no true ccenenchyma. Some 

 of the Rugosa are simple ; but others are composite, increasing 

 either by parietal or by calicular gemmation. 



Recently it has been shown that some very abnormal Rugose 

 corals were provided with a lid or operculum, closing the mouth 

 of the calice. In the genus Calceola (fig. 51), formerly referred 

 to the Brachiopoda, and very abundant in certain parts of the 

 Devonian System, the operculum consisted of a single valve or 

 piece. In Goniophyllum four valves were present, and in 

 Cystiphyllum prismaticum there were four or more valves in 



