GENUS ORBITOLITES: — HISTORY. 
189 
{op. cit.), on the authority of a voyager in the Indian seas, that living Discolites 
have been found there ; and as there are no existing Nummulites, this statement 
probably refers to an Orbitolite. Lamarck, in his second edition, describes, under 
the title of O. marginalis, a small form of Orbitolite, only 2 millirns. (‘08 inch) in dia- 
meter, found upon fuci, corallines, &c, in the European seas ; this he speaks of as 
the only living example of the genus then known, and he defines it as O. utrinque 
plana, marglne poroso. Besides this species, however, Defrance {loc. cit.) mentions 
another, more closely resembling the O. complanata of the Paris basin, as existing on 
the shores of New Holland ; and this seems the first clear indication of the body 
(afterwards found by MM. Quoy and Gaimard in that locality, and erected by them 
into the distinct genus Marginopora), the structure of which constitutes the chief 
subject of my present communication. Both these existing forms are described by 
Blainville {op. cit.), the first from actual observation, the second on the information 
of MM. Quoy and Gaimard, to the manuscript of whose ‘Voyage de I’Astrolabe’ 
(then unpublished) he refers as his authority. It is singular, however, that after an 
attentive search through the published “Zoology” of that work, I have not been able 
to find, either in the text or in the plates, any mention of Marginopora or of Orhito- 
lites. Of the OrhitoUtes marginalis, M. de Blainville says {op. cit. p. 412), — “ Nous 
I’avons etudiee avec soin ; et nous sommes presque convaincu que ces petits corps 
cretaces ne sont pas de veritables polypiers ; mais bien quelque pi^ce interieure, qui 
s’accroit par la circonference. II est en eflfet evident, qu’il n’y a pas de cellules pro- 
prement dites, a moins qu’on ne veuille regarder comme telles les deux plans de 
locules qui occupent le bord, et qui n’oflfrent rien determine. Tout le reste est cou- 
vert d’une legere croiite cretacee, qui ferme les anciens pores.” I think it obvious, 
from this description, that it was founded on specimens resembling that in Plate VII. 
fig. 8, in which the marginal row of cells has been laid open above and below by 
accidental abrasion ; and that the true marginal pores, opening between the protu- 
berances formed by the cells (Plate V. fig. 1), were overlooked. The genus Margi- 
nopora, placed by M. de Blainville in immediate sequence to Orbitolites, is thus 
characterized {loc.cit.)-. — “ Animaux inconnus, contenus dans les cellules poriformes, 
excessivement petites, rondes, serrees, eparses dans les sinuosit^s, tres fines et tor- 
tueuses, qui guillochent la circonference d’un polypier calcaire, libre, un peu irre- 
gulier, discoide, concave ou concentriquement strie en dessus comme en dessous, et 
plus epais sur les bords.” The two surfaces, M. de Blainville further tells us, only 
exhibit striae of increase, without any trace of pores; but the turned-iip edge is 
entirely riddled with very fine rounded pores, which are situated in the sinuosities of 
a very close but shallow engine-turning (guiilochis). And when one of its surfaces 
is rubbed away, the disk is found to be formed of concentric canals, separated by 
partitions, and themselves divided into cells, thus recalling in some degree the struc- 
ture of Orbitolites. Having myself had the opportunity of inspecting, by the kind- 
ness of M. Valenciennes, the specimens of Marginopora on which the foregoing 
2 c 
MDCCCLVI. 
