xlii THE VOYAGE OF H.M.S. CHALLENGER. 



laid together so as to close over the oral cavity as with an operculum. The coenenchyma 

 and polyps are covered with a layer of scales, the margins of which are dentate. In 

 the third subfamily, the Isidinse, the polyps are sunk into a thick coenenchyma, and no 

 external calyces have been developed. 



Subfamily 1. Ceratoisidin^. 



1. Bathygorgia,VQXC&y&\ Wright. 



2. Ceratoisis, Perceval Wright. 



3. Callitsis, Verrill. 



4. Acanella, Gray. 



5. Isidella, Gray. 



6. Sclerisis, Studer. 



Subfamily 2. MopsEiNiE. 



7. Primnoisis, Wright and Studer. | 8. Mopsea, Lamouroux. 



9. Acanthoisis, Wright and Studer. 



Subfamily 3. Isidin^e. 

 10. Isis, Linneus. 



Subfamily 1. Ceratoisidin.e. 



Kercdoiddae, Gray, Cat. Lithophytes Brit. ^lus., 1870, p. 18. 



Acanelladae, Gray, torn, cif., p. 16. 



Mopseadse, Gray, torn, fit., p. 13. 



Ce)-atoisidx, Verrill, Bull. Mus. Conip. Zoo!., vol. xi. p. 9, July 1883. 



The colonies are simple, rod-like, or branched ; they rise from a calcareous base 

 usually ramified into root-like processes. The calcareous internodes are very long in 

 comparison with the horny nodes, and in the younger portions are penetrated by a 

 canal. The coenenchyma is thin ; the polyps are long, and imperfectly or non- 

 reWactile. The tentacles when at rest are folded over the oral disc or sometimes 

 partially invaginated. The coenenchyma and polyps, and sometimes also the polyp 

 tentacles, are covered with large, smooth, needle- or spindle-shaped spicules. 



1. Bathygorgia, Perceval Wright, Narr. Chall. Exp., vol. i. p. 691, fig. 236. 



The colony is unbrauched, the axis consists of very long calcareous internodes, and 

 short horny nodes. The polyps arise only on one side, are large in size, somewhat 

 constricted medianly, and thickened towards base and apex. The tentacles at rest lie 

 folded horizontally over the oral disc. Coenenchyma and polyps are covered with flat 

 smooth spicules of a long oval form. These lie transversely in the tentacles, one or 

 two occupying the breadth of each. On the polyps, over the layer of small spicules, 

 some large, obliquely or longitudinal placed spicules, club- or biscuit-like in shape, are to 

 be found. 



