76 THE VOYAGE OF H.M.8. CHALLENGER. 
development of vesiculate endotheca, the series of calicinal centres are separated by wide 
ridges, formed entirely by the thin wall and by the convex dissepiments which stretch 
from the centre to this thin wall. 
This genus, which has been confounded by Milne-Edwards and Haime with Plerogyra 
will include not only the following species, but also the Plerogyra lichtensteini of those 
authors ; the genus Plerogyra being limited to those forms in which the walls are not 
fused throughout so as to form a thin lamina, but in which the series remain distinct: 
with their walls united below and separated above, except occasionally when two free 
growing ends meet, and grow together. 
Physogyra aperta, Quelch (Pl. IIL. figs. 1-1a). 
Physogyra aperta, Quelch, Ann, and Mag. Nat. Hist., vol. xi., 1884, p. 294. 
Corallum convex above; wall very thin, simple, sometimes almost rudimentary. 
Costze very slightly developed, and then only at the margin of the series. The series of 
the calicinal centres open and shallow, in no part deep and narrow ; the centres are often 
difficult to distineuish, owing to the uniform development of dissepiments along the 
series. Width of series about 16 mm., but at times more than 20 mm. The septa are 
from 2 to 4 mm. apart, very thin and very projecting, subequal except at the ends of 
the series where some are very small, fragile and easily broken away, leaving the vesicular 
dissepimental ridges almost bare. The dissepiments are thin, convex above, more or less 
fragile and easily broken away, about 3 mm. apart from those above or below at the wall, 
closer at their inner terminations, forming simple, wide, curved interseptal chambers. 
The species is easily distinguished from the Physogyra lichtensteini (Milne-Edwards 
and Haime) by the nature of the calicinal centres which in that species are very deep 
and narrow. 
Locality.—Banda. 
Genus 6. Pectinia, Oken. 
Pectinia (pars), Oken, Lehrb. der Naturg., i. p. 68, 
ay Milne-Edwards and Haime, Cor., ii. p. 206. 
FA Dunean, Rey. Madrep., p. 86. 
The dissepiments in this genus are stated by Milne-Edwards and Haime to be very 
abundant, curved and oblique, sometimes simple but more often forming large vesicles. 
This, however, is misleading, for in the calicinal valleys very little can be seen of 
endotheca as viewed exteriorly, and it is only at the basal parts, as seen in section, that 
the endotheca can be made out. In young stages, therefore, no endotheca, or but 
very slight traces of it at the base, would be present. 
