1899.] ASTR^XD CORALS FROM THE SOUTH PACIFIC. 757 



the colmnella. The secondary septa also join the cohmiella, but 

 never have marked pahform teeth. The tertiary septa are very 

 narrow, except where two quaternary septa are present on either 

 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 1 mm. across, and is formed by a few coarse trabeculse 

 from the primary septa. 



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

 diameter, 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 

 thecsB and costae completely filled up by exotheca. 



Genus PRIONASXR.ilA. 



Pnonastr<xa, Milne-Edwards & Haime, Comp. rend, de I'Acad. 

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



Acanthastrcea, Milne- Edwards & Haime, Comp. rend, de l'A(;ad. 

 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 long^-st near the columella in 

 P/'ionastrcea, and shortest in the same position in Acanthastrcea. 



Martin Duncan, in his " Revision of the Families and (xenera 

 of the Madreporaria," ^ added no new constant chai'acters, but 

 placed the t\vo genera in different alliances, which he described 

 in diiferent but practically synonymous terms. In the specimen 

 referred by me 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 1 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 my collection 

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

 and body-wall being thrown iuto blunt rugae between the attach- 

 ments of tlie mesenteries. 



1 Journ. Lino. Soc, Zaol. xviii. pp. 119 & 123 (1885). 

 Pi^oc. ZooL. Soc— 1899, Xo. XLIX. 49 



