xvill BRITISH FOSSIL CORALS. 
§ 2. Wall completely covered by a pellicular epitheca. 
22. Genus FLABELLUM. 
Lesson, Illustr. de Zoologie, 1831; Phyllodes, Philippi, Neues Jahrbuch fiir Miner. Geol. 1841. 
Corallum simple, compressed, and in general free in the adult state. Cadice usually 
elliptic, very strongly arched in the direction of its long axis; fossula narrow, and very 
deep. Columella spurious, and formed by marginal trabicule of the septa; very little 
developed, or even quite rudimentary. Sep/a in general very numerous, appertaining in 
reality to six primitive systems, but forming in appearance a much greater number of 
systems ; not projecting above the margin of the wall, and presenting laterally regular rows 
of well-developed granulations. Walls completely covered with a thin, slightly-striated 
epitheca, and in general armed laterally with long spiniform processes, corresponding with 
the direction of the long axis of the calice. No radiciform appendices. 
Typ. sp., Flabellum pavoninum, Lesson, op. cit., pl. xiv. 
23. Genus PLACOTROCHUS. 
Milne Edw. and J. Haime, loc. cit., p. 282, 1848. 
Corallum resembling much those of the preceding genus, but having a lamellar 
columella. 
Typ. sp., Placotrochus levis, Milne Edw. and J. Haime, loc. cit., tab. viii, fig. 15. 
24. Genus BLASTOTROCHUS. 
Milne Edw. and J. Haime, p. 282, 1848. 
Corallum resembling those of the genus Flabellum, but gemmiparous ; the young pro- 
duced by buds placed along the lateral edges of the corallum, and becoming free by the 
progress of their development. 
Typ. sp., Blastotrochus nutrix, Milne Edw. and J. Haime, loc. cit., tab. vili, fig. 14. 
25. Genus RutzoTRocHts. 
Milne Edw. and J. Haime, loc. cit., p. 281, 1848. 
Corallum simple, trochoid, and adherent by means of cylindrical radiciform appendices, 
which proceed from the wall, at different heights, and descend to embrace the extraneous 
body on which the Zoophyte lives. Cadice almost oval, with a very narrow and very deep 
fossula. No columella. Septa extending to the middle of the visceral chamber, where they 
unite without presenting any trabicule. 
Typ. sp., Rhizotrochus typus, Milne Edw. and J. Haime, loc. cit., tab. 8, fig. 16. 
