218 Christmas Island, 



secondary septa are long and thin, the latter being considerably the- 

 shorter ; both are connected to the columella, though in sections* 

 the connection may not be shown in all cases. 

 Dhtrihxdion. — Christmas Island. 

 Fossil : 



Xo. 946. From the limestone pinnacles a little south 



of the middle of the island : alt. 550 feet. 



IS'o. 511. A specimen from top of the upper cliff, 



middle of the east coast. 



Figure. — PI. XIX, Fig. 4. Part of a transverse section of 



specimen Xo. 946, x 2 dia. 



Affinities. — Orhicella prceheliopora is a species inteiTtiediate in 

 characters between the Orhicella irregularis (Mart.) fi^om the 

 Pliocene of Java and 0. heliopora (Lam.) from the Australian 

 seas. It is probably nearer the former, which differs by having 

 only four cycles of septa, and by having the corallites crowded 

 together so that they are iiTegular and polygonal in shape. The 

 two species agi^ee ia the irregularity of the septal sequence. In 

 two adjacent sectors in one coralHte of the type-specimen of 

 0. praiheliopora the sequence is as follows : — 



1 4 3 2 5 3 1 

 16473525341 



According to Martin's diagram of 0. irregularis, the sequence 

 in three sectors in that species is : — 



13 2 3 1 



14 3 5 2 3 1 

 1 3525341 



From 0. heliopora the Christmas Island coral differs by having 

 a looser columella and less regular septal sequence ; for 0. heliopora 

 is said to have four complete cycles. The primary, secondary, and 

 tertiary septa are said, moreover, to be not very different in size 

 in the living species. 



Acanthastrsea patula (Dana). 



Orhicella patula, Dana, 1848. Zooph. : Eipl. Eiped. "Wilkes, vol. viii, p. 209, 



pi. X, fig. 14. 

 AcanthastrcBa ? patula, Edwards <S:Haime, 1857. Hist. nat. Cor., vol. ii, p. 505. 



Yar. pancidentata, nov. 



The genus AcayithaitrcBa is represented in the collection by 

 a small fragment 70 mm. long ; the coraUites are from 9 to 12 mm. 

 in diameter, the majority being 12 mm. The columella is small, 

 and consists of a few denticles, though sections at first sight 

 appear to have a long columella owing to the abundance of central 



