Madreporarian Genus Turbinaria. 511 



it is exactly in this case that the specific value of methods of 

 growth appears to break down, for we find specimens which 

 all appear to belong to one species, viz. Turhinaria peltata^ 

 forming on the one hand enormous hemispherical masses * 

 and on the other hand systems of erect fronds. 



Whether this particular " species " ought to be further 

 broken up according to the different methods of growth it 

 presents I find it very difficult to decide. There are tliirty 

 specimens apparently belonging to it in the National Col- 

 lection, showing every stage of growth between the two 

 extremes mentioned. Taking the coralla alone into account, 

 it does not seem practicable to divide them. Perhaps when 

 the living corals are studied, important differences which 

 would justify their separation may be found. 



The large specimens show that as the old stocks die down 

 they are overrun by fresh layers of living coral. The dying 

 down spreads gradually over the surface, and then the dead 

 surface is gi'own over again by a fresh layer starting from 

 some still living portion. In this way great hemispherical 

 masses are produced by layer overgrowing layer. The layers 

 themselves, however, are not thickened. This fact distin- 

 guishes these often glomerate masses from the true glomerate 

 type of growth, in which each layer is itself enormously 

 thickened in the centre and forms a hemispherical mass 

 (PI. XIX. fig. 7). 



Third Type of Groioth : Frondens. — This method of growth 

 seems to originate from a deep bowl-shaped cup, the margin 

 of which grows vertically. The constant lengthening of the 

 circumference by the formation of new buds, while the form 

 of the cup does not admit of any great enlargement of the 

 circumference, leads to the breaking-up of the margin into 

 lobes which roll inwards and curl round. Complicated 

 masses of erect fronds, some spirally coiled, may thus arise. 

 I understand this to be what Dana meant by " cucullately " 

 folded. This group is established to take Dana's species 

 T.frondeMS and a few specimens in the National Collection 

 which approach this method of growth. 



In these forms accessory lobes seem often to spring out 

 from the faces of the fronds. These were either once mar- 

 ginal, the edge having again united, or are true accessory 

 outgrowths, which are perhaps to be associated with the 

 hindering of the downward flow of the coral-substance. In 



* Two magnilicent specimens illustrating this method of growth, sent 

 by Mr. Saville Kent from the Great Barrier Reef, are mounted in the 

 public galleries of the Natural History Museum. 



