7. Anthozoa (incl. Hydrocorallia). A. Zoantharia. 31 



not only the part covered but also a large surrounding area. A similar con- 

 dition was noticed in a Forties covered by a Pavonaria, and a Madrepora 

 attacked by a Montipora is also described. The observations show that when 

 two Madreporaria are on the same support and contend for position the en- 

 crusting form prevails, killing its adversary by enveloping it; the massive 

 and globular forms succumb most quickly in the struggle, the arborescent 

 forms can resist longer. 



Gravier( 3 ) describes the habitat of Siderastrea at San Thome [see Bericht f. 

 1908 Coel. p 31] and points out the great difficulty in distinguishing radians 

 and siderea. The configuration of the calices seems to be intimately corre- 

 lated with the conditions; if the coral is under favourable conditions (i.e., in 

 clear water) the calices assume the hexagonal form and the internal edges of 

 their septa slope to the bottom: when the coral is living in water with much 

 sediment the regularity of contour of the calices disappears and the edges of 

 the septa become perpendicular to the basilar plate. The diameters of the 

 calices do not furnish clear distinguishing characters; the columella is scarcely 

 more reliable, nor is the number of septa. S. r. and s. may be only two 

 facies of the same species. - - See also Gravier( 2 , 4 , 8 ~ 10 ). 



Gravier( 1 ) points out that while coral reefs are relatively poorly developed 

 on the west coast of Africa, there may probably be extensive submerged coral 

 patches. He records from San Thome and Prince Islands, Gulf of Guinea, 

 Maandra cerebrum, Favia fragum, Orbicella annularis (1 n. var.j Siderastrea 

 radians, Oculina arbuscula and Porites bernardi. 



Howchin records, from off Glenelg, Gulf St. Vincent, South Australia, a large 

 mass, 7x4 1 / 2 >< 3 1 /2 feet, of Plesiastrcea urvillei, apparently of great age. The 

 greater part of the mass was dead. 



Jones ( 2 ) argues that Darwin's theory of subsidence will not explain the origin 

 of Cocos Keeling atoll, as the lagoon has steadily become shallower since 

 1825 and the structure of the reef shows that there has been no sinking from 

 the time the reef first reached the surface of the sea. Murray's theory of 

 solution will not explain the origin of the atoll, for deposition of calcium car- 

 bonate is taking place everywhere in the lagoon area and coral sand is con- 

 stantly accumulating in the lagoon. The author puts forward his view that 

 sedimentation takes the largest share in the production of most of the stages 

 of an atoll [see Bericht f. 1909 Coel. p 51]. See also Hartmeyer and 

 Jonesi 1 ). 



Brown derives Streptelasma from a hypothetical early Ordovician ancestor 

 Protostreptelasma having a hollow conical, or horn-shaped calyx, 



straight or slightly curved, without septa or having only a few ridges, near 

 the upper margin, indicative of septa. In the ontogeny of Sir. the non- 

 septate condition is soon passed and in the later stages the well developed, 

 tetramerally arranged septa are the most prominent character. Four primary 

 septa first appear, followed by secondary septa added in pairs in the counter 

 and cardinal quadrants; tertiary septa appear, in the inter-septal spaces, in 

 the same order as the secondary. The first pair of secondary septa in the 

 counter, and the first pair in the cardinal quadrant are added simultaneously, 

 whereas in the geologically later species of the Sir. group the first pair of 

 secondary septa in the counter quadrants is invariably added before the first 

 pair in the cardinal quadrants. This acceleration is observed in the upper 

 Ordovician corniculum and rusticum and is still more marked in the Silurian 

 Enterolasma caliculum, in which it increases progressively during the life of 

 the individual, becoming strongly marked during the later stages of growth. 



