J 899.] ASTR.IID CORALS PROM TUB SOUTH PACIFIC. 757 



the coUtmella. The secondary septa also join the coluiuella, but 

 never have marked palifonn teeth. The tertiary septa are very 

 narrow, except where two quaternary septa are present on eithef 

 side. Both septa and costse are relatively thin and are covered on 

 their edges by low, blunt, subequal teeth. The columella is seldom 

 more than I mm. across, and is formed by a few coarse trabeculje 

 from the pi'iraary septa. 



The calices, when round, are seldom more than 7 mm. in 

 diiuneter, but some of oval shape are 9 mm. long by 5 mm. broad. 

 The depth of all is fairly constant, 3-4 mm. 



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 through- 

 out, but the latter is much denser, with the spaces between the 

 thecae and costse completely filled up by exotheca. 



Genus PrionastrjEA. 



Prionastrcea, Milne-Edwards & Haime, Comp. rend, de I'Acad. 

 des Sc. xxvii. p. 495 (1848), and Cor. ii. p. 513 (1857). 



Acantlmstrcea, Milne- Edwards & Haime, Comp. rend, de I'Acad. 

 des Sc. 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 Jcanthastrcea. 



Martin Duncan, in his " Eevision of the Families and Grenera 

 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 me to P. ecTiinata, 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 

 duy, 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 pnd round it. 

 Tn P. abdita I observed short "blunt processes of the bod7-wall 

 round the peristome ; but in the spirit-specimens in my collection 

 there is no trace of these rudimentary tentacles, the whole peristome 

 and body- wall being thrown into blunt rugte between the attach- 

 ments of the mesenteries. 



^ Jonrn. Linn. Soc, Zool. xviii. pp. 119 & 123 (1886). 



Peoc. Zool. Soc— 1899, ^o. XLIX. 49- 



