} BRITISH FOSSIL CORALS. 
20. Genus PACHYSERIS. 
Milne Edw. and J. Haime, loc. cit., p. 72, 1849. 
Corallum similar to Agaricia, excepting that the corallites belonging to the same 
trench are completely blended together.  Co/wmella well developed and dense. 
Typ. sp., Pachyseris rugosa, nob. ; Agaricia rugosa, Lamarck, Hist. des An. sans Vert., t. ii, p. 243. 
21. Genus PHYLLASTREA. 
Helioseris, Dana, Zooph., p. 269; Milne Edw. and J. Haime, loc. cit., p. 72, 1849. 
Corallum composite, composed of frondiform expansions. Ca/ices circumscribed, sub- 
mamumillate, and arranged around the parent corallite, which remains larger than the others. 
Columella tubercular. 
Typ. sp., Phyllastrea tubifex, Dana, loc. cit., tab. xvi, fig. 4. 
22. Genus HanosEris. 
Milne Edw. and J. Haime, loc. cit., p. 72, 1849. 
Corallum composite, forming foliaceous, crispate, lobulate expansions, the upper surface 
of which is covered with very long radii, and shows only obsolete calices. Columella 
rudimentary. 
Typ. sp., Haloseris lactuea, Milne Edw. and J. Haime, loc. cit. 
23. Genus LEPTOSERIS. 
Milne Edw. and J. Haime, loc. cit., p. 72, 1849. 
Corallum composite and adherent; the basal walls rising so as to constitute a sub- 
crateriform disc, in the centre of which is situated a large parent corallite, surrounded by 
smaller ones. Ca/ices very imperfectly circumscribed, but well radiated. Septa very long. 
Columella radimentary. 
Typ. sp., Leptoseris fragilis, Milne Edw. and J. Haime, loc. cit. 
Sub-order 2. 
ZOANTHARIA PERFORATA. 
Corallum composed essentially of porous sclerenchyma; with the septal apparatus well 
characterised, and consisting of six primitive elements, but being sometimes represented 
only by series of trabicule. Dissepiments rudimentary ; no tabule. 
The principal character of this section of Zoantharia is furnished by the structure of 
