DESCRIPTION OF CHALK CORALS. 299 
having been fully detailed; but the external lamina is believed to constitute a 
most marked distinction from Rosacilla; and even if the minuteness of Ros. 
serpulaformis prevented its being detected, still should it exist, as such a struc- 
ture does not enter into the generic characters, nor is noticed in the descriptions 
of the species, its presence would rather justify a separation of that coral from 
Rosacilla, than a union of the chalk fossil with Herr Roemer’s genus. Among 
Tubuliporide which exhibit partial agreements with the subject under consider- 
ation, as a similar arrangement of the apertures, accompanied by an external 
lamina, may be mentioned the Obelia of Lamouroux'; but that genus has been 
united by M. Milne-Edwards* to Tubulipora (T. verrucaria) and the lamina, 
instead of being tubular, is minutely foraminated similarly to the tubes themselves. 
As respects Tubulip. patina, the area occupied by visceral cavities is surrounded by 
a delicate zone traversed by radiating lines, and presenting an appearance some- 
what resembling that of the exterior layer of the chalk fossil ; but in the recent 
zoophyte the marginal plate is a dorsal or inferior, not an upper structure ; and 
the strize instead of indicating microscopic tubes are, for the most part, at inter- 
vals equivalent to the breadth of visceral cavities ; and they define in some En- 
glish specimens usually assigned to the species, the commencement of side walls 
to future tubes*. Sometimes only a very narrow interval is visible between ad- 
jacent striz, the precursor apparently of an interpolated abdominal receptacle. 
The upper lamina of this coral, designed, it is conceived, to support the protruded 
portion of the tubes, is moreover minutely foraminated as in the case of Lamou- 
roux’s Obelia ; nor can the depressed openings or “ sorte de tissue aréolaire de 
consistence pierreuse”’ of M. M.-Edwards', and observable in some British spe- 
cimens, be regarded as an equivalent structure to the surface layer of the creta- 
ceous zoophyte, not being of constant occurrence, and exhibiting distinct aper- 
tures, whereas the microscopic tubuli of the chalk fossil are closed at their extre- 
mity. Another coral which resembles in the surface arrangement of the tubes 
or cells, the organic body under examination, is a tertiary production to which M. 
Michelin® has applied the term Adeona lamellosa, though possibly without being 
perfectly assured of the generic identity: it is sufficient for the present inquiry 
‘ Exposition Méthodique, p. 81. tab. 80. figs. 7, 8. 
> Ann. Se. Nat. 2nde série, Zool. tome viii., or Recherches sur les Polypes, Mém. sur les Tubulipores, 
p. 7-8. 5 Consult Milne-Edwards, op. cit. pl. 13. fig. 1. 
‘ Dr, Johnston’s Brit. Zoophytes, Ist edit. pl. 31. figs. 2, 3; and 2nd edit. pl. 47. figs. 2, 3. 
° Op. cit. p. 9. pl. 13. fig. 1. ®° Icon. Zoophyt. p. 326, pl. 78. fig. 5. 
