96 ; THE VOYAGE OF H.M.S. CHALLENGER. 
3. Hydnophora tenella, n. sp. (Pl. V. figs. 88a). 
Corallum extremely thin, forming irregularly bent and undulate plates, which are 
neither incrusting nor thickened at the middle, nor lobate above. The under surface 
irregularly costate, being finely striated and furnished with a thin epitheca. On the 
upper more flattened surface the calicinal centres are generally very distinct, but become 
much less so on those parts which are bent downwards. Where the centres are distinct 
the septa are of three cycles, the last being incomplete, and the little cones or monticules 
are very low and broad, and almost rounded, having the septa which traverse them 
narrow and far apart, with wide vesicular interseptal chambers, formed by numerous 
well-developed dissepiments. At the centre of the calicles and in the valleys the septa 
are coarsely granulated, and give the appearance of a well-developed columella. The 
monticules may be conical or much elongated; and towards the margin they become 
sharp, angular, and rather narrow, and much more elevated than at the central portion 
of the colony. At the central portions the calicles in the same series are from about 
4 to 5 mm. apart; the width of the monticules being from about 5 to 6 mm., and the 
height from 1 to 2 mm. 
A single specimen was obtained. 
The species is close both to the Hydnophora exesa and Hydnophora demidofji, but is 
distinguishable by the free, contorted, thin, explanate habit, by the nature of the calicinal 
centres which are more clearly astreeiform than in any other species of the genus, and by 
the wide, flattened and vesicular monticules. 
Locality.—Samboangan, Philippines. 
Genus 18. Astrwa, Lamarck. 
Astrxa, Lamarck, Syst. Anim. sans Vert., p. 371, 1801. 
Favia, Milne-Edwards and Haime, Cor., ii. p. 426. 
» Dunean, Rev. Madrep., p. 100. 
Following Verrill, I have retained for this group Lamarck’s Astrea, which undoubtedly 
claims priority over the Favia of Oken. The type of Lamarck, for which the name Astrea 
should have been retained, was the Astrxa rotulosa of his first section and not the Astrea 
(Siderastrea) galaxea of the second, to which Oken applied it. 
Ten species are in the collection. 
1. Astrea fragilis, Dana. 
Astrea fragilis, Dana, Zoophytes, p. 230, pl. xii. fig. 2. 
This species is widely separated from the Astrea dipsacea, to which Dana had 
likened it, and which has since been referred by Verrill to the genus Acanthastrea. 
