Skeletal variation in two large coralla from Tahiti, one of Pavona varians (Verrill) and another of Psammocora haimiana Milne Edwards and Haime

Abstract

The corallum of Pavona varians (Verrill) (plate 15, figure 1, plate 16, figures 3, 4, 5, 9 and 10) is 23 cm. in length and 22 cm. in breadth, incrusting, rising into hillocks up to 3 cm. in height and 2-5 or 3 cm. in thickness over the greater part of the calicinal surface, hence corallum appears to be very irregular. On the hillocks valleys are sinuous, width about 3 mm., depth about the same. Colline is 1.5 mm. in thickness. The highest part of a hillock ends in a colline which then appears as a ridge. Septa are in two regular series, alternately broad and narrow, continuous over colline, hence forming an alternating series over the colline also. Inner margins of septa are almost entire, sides spinulose. Septa, after curving over colline, drop vertically down. Columellar centres are inconspicuous, appearing to be solid, ridged above; neighbouring centres are directly linked by 1 to 3 septal lamellae. When valleys are broader, more than one row of columellar centres are present along the base; centres tend to occur also on the sides of colline. This is the typical P. varians facies.