lxxviii BRITISH FOSSIL CORALS. 



12. Genus Xenia. 



Savigny, Egypte, Atlas and op., Lamarck, op. cit., vol. ii, p. 629, 1816. 



Polypi forming subramified masses, as in Alcyonium, but not retractile, and not having 

 a thick coating of spiculse at the basis of the tentacula. 



Typ. sp. Xenia umbellata, Savigny, Egypte, Polyp., tab. i, fig 3. 



13. Genus Nephthya. 



Savigny, Atlas de l'Egypte- Blainville, Manuel d'Actinol, p. 523; Spoggodes, Lesson, Illustr. de 



Zoologie, 1831. 



Polypi forming arborescent masses, incompletely retractile, and having the borders of 

 the calice thick and incrustated with large navicular spiculae. 



Typ. sp,, Nephthya Chabroli, Aiulouin, ap. Saviguy, Egypte, Pol. tab. ii. fig. 5. 



14. Genus Paralcyonium. 



Alcyonidia, Milne Edwards, Ann. des Sc. Nat. 2d series, vol. iv, p. 323. 



Polypi resembling Nephthya, but being completely retractile, and having the lower 

 part of the common mass incrustated with a thick coating of long navicular spiculse, but 

 the upper part membranaceous and retractile. 



Typ. sp., Paralcyonium elegans ; Alcyonidia elegans, Milne Edwards, loc. cit., tab, xii and xiii. 



15. Genus Sarcophyton. 



Lesson, Zoologie du Voyage de la Coquille, Zooph., p. 92, 1831. 



Differs from the genus Alcyonium by the great abundance and the peculiar structure 

 of the common tissue, the cells of which are tubular, and arranged with great regularity 

 in fasciculi, perpendicularly to the upper surface of the mass. 



Typ. sp., Sarcophyton plicatum, Valenciennes MSS. ; Sarcophyton lobulation, Lesson, loc. cit. ; Alcyo- 

 nium plicatum, Lamarck, Hist, des An. sans Verteb., vol. ii, p. 395. 



16. Genus Cespitularia. 



Valenciennes MSS. 



Polypi non-retractile, arranged in fasciculi, and united in the greatest part of their 

 length by a dense, tough, common tissue, as in Alcyonium. 



Typ. sp., Cespitularia multipinnata, Valen. ; Cornularia multipinnata, Quoy and Gaimard, Voyage de 

 I'AstroIabe, Zooph., tab. xxii, figs. 1-4. 



