TURBINARI^ PELTIFORMES. 43 



Species I'J. Turbinaria orbicularis. (PL XXXI. fig. 17.) 



Description. — Corallum peltate, slightly concave in the centre, while the edges grow out 

 horizontally. Edge of corallum thin, composed of a row of liudding calicles. It is con3e(|uently 

 deeply wrinkled on the under surface for about half an inch. 



Calicles large (3 mm.), though varying ia size, the margin only protuberant as thin elliptical 

 rings about 1 mm. high. The rather solid coenenchyma of the outer layer of this wall changes 

 suddenly into the ring of short, thin septa. Tiie number of these depends upon the size of the 

 calicle, the largest having 34 to 40, the smaller, 24. They fall far short of the half-radius 

 circle, and slope gradually down round the deep, open, slightly funnel-shaped fossa. The 

 columella is very conspicuous and protuberant, almost ball-like. 



The ccenenchyma is a rather coarse, solid reticulum, tending here and there to form a 

 typical ridge-and- furrow system. 



There are three specimens, perhaps too young to classify, which I have associated together 

 under this heading. Their edges have unfortunately been much broken owing to their 

 thinness. The largest appears originally to have been a circular plate, 10 cm. across, with 

 a slight depression immediately above the short, thick stalk. One of the smaller specimens 

 (6 cm.) has a thinner stalk, but otherwise agrees in almost all essentials with the type. The 

 other shows a slight tendency of the margin to fold, and may be a young specimen of T. con- 

 sjiicua. The most conspicuous differences between the specimens is in the fine texture of the 

 columella. In the largest specimen the columella becomes granular, whereas in the smaller it 

 remains foliate, in some cases with a peculiar twist in it as if it had been stirred round, which 

 is probably another expression of the tendency to a spiral twist noticed in the introduction 

 (p. 13). 



The central calicles iu the larger specimens are immersed, and face directly upwards ; the 

 outward slope commences near the edge along which the young calicles are budding quite 

 horizontally. This species thus affords an excellent illustration of the bending up of the 

 calicles as they grow, in order to allow the next buds to continue in approximately the same 

 plane of growth. 



One edge of the larger specimen has been greatly distorted by Balanids. 



«. King's Sound, West Australia. Saville-Kcnt Coll. (Type.) 



h. King's Sound, West Australia. Saville-Kent Coll. 



c. Somerset Shore, Cape York. H.M.S. ' Challenger.' 



Species 20. Turbinaria radicalis. (PI. IX. ; PI. XXXI. fig. 18.) 

 Description. — Corallum a flat circular disc, with slight tendency to form protuberances. 

 As it spreads over the substratum, it sends down finger-shaped processes like roots, which 

 may secondarily branch. These become attached to the substratum. Free margin of the 

 disc tliin. 



Calicles crowded, projecting as blunt cones in parts, especially on slight elevations. 

 Apertures circular or slightly elliptical (2 mm. and under). Septa (16, here and there 24) 

 project to about the half-radius circle ; in the projecting calicles the upper edges of the septa 



G 2 



