xviii BRITISH FOSSIL CORALS. 



§ 2. Wall completely covered by a pellicular epitheca. 



22. Genus Flabellum. 



Lesson, Illustr. de Zoologie, 1831 ; Phyllodes, Philippi, Neues Jahrbuch fur Miner. Geol. 1 84 1 . 



Corallum simple, compressed, and in general free in the adult state. Calice usually 

 elliptic, very strongly arched in the direction of its long axis ; fossula narrow, and very 

 deep. Columella spurious, and formed by marginal trabiculae of the septa ; very little 

 developed, or even quite rudimentary. Septa 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., pi. 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 Icevis, 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. viii, fig. 14. 



25. Genus Rhizotrochus. 



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. Calice 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 trabiculse. 



Typ. sp., Rhizotrochus ty pus, Milne Edw. aud J. Haime, loc. cit., tab. 8, fig. 16. 



