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Show 1 899.] ASTR.E1D CORALS FROM THE SOUTH PACIFIC. 757 the columella. The secondary septa also join the columella, but never have marked paliform teeth. The tertiary septa are very narrow, except where two quaternary septa are present on either side. Both septa and costae are relatively thin and are covered on tiieir edges by low, blunt, subequal teeth. The columella is seldom more than 1 m m . across, and is formed by a few coarse trabeculae troin the primary septa. The calices, when round, are seldom more than 7 m m . in diameter, but some of oval shape are 9 m m . long by 5 m m . broad. The depth of all is fairly constant, 3-4 m m. Funafuti; leeward reef. There are two specimens of this species, one of which is 14 by 9 cm. by 7 cm. high, and the other a small colony, 6 by 5 by 3 cm. high. The former is of a light structure throughout, but the latter is much denser, with the spaces between the theca) and costae completely filled up by exotheca. Genus PRIONASTRCEA. Prionastrcea, Milne-Edwards & Haime, Comp. rend, de l'Acad. des Sc. xxvii. p. 495 (1848), and Cor. ii. p. 513 (1857). Acanthastrcea, Milne-Edwards & Haime, Comp. rend, de l'Acad. des S c xxvii. p. 495 (1848), and Cor. ii. p. 501 (1857). The species described by Milne-Edwards and Haime under these two genera were practically separated solely by the septal teeth. These were said to be longest near the columella in- Prionastrcea, and shortest in the same position in Acanthastrcea. Martin Duncan, in his " Revision of the Families and Genera of the Madreporaria," * added no new constant characters, but placed the two genera in different alliances, which he described in different but practically synonymous terms. In the specimen referred by m e to P. echinata, while generally the septal teeth are longest over the walls, in some calices they are of nearly equal length and in a few absolutely longest near the columella. The opposite too is true of P. abdita and P. purpurea. I found also in specimens of both the so-called genera in the British Museum nearly every possible variety in arrangement of the septal teeth. Although I had different species of this genus constantly under observation, both on the reef and in bottles, both by night and by day, it is noticeable that I never saw any polyps with'well-marked tentacles. The peristome in all living polyps is quite distinct and smooth, while the external body-wall forms a thick pad round it. In P. abdita I observed short blunt processes of the body-wall round the peristome; but in the spirit-specimens in m y collection there is no trace of these rudimentary tentacles, the whole peristome and body-wall being thrown into blunt rugae between the attachments of the* mesenteries. 1 Journ. Linn. Soc, Zool. xviii. pp. 119 & 123 (1886). PROC. ZOOL. Soc-1809, No. XLIX. 49 |
