452 PERCY SLADEN TRUST EXPEDITION 



forms (repens) and the branching forms (ramosum). The same remarks apply to the 

 genus Homotrema. I can recognise in this genus only one species H. rubrum and two 

 facies repens and ramosum. 



The question of colour is an important but difficult one. The colour of Polytrema 

 miniaceum and the colour of Homotrema rubrum are remarkably constant (cf. p. 446). 

 In these species neither yellow nor orange coloured varieties have been observed. White 

 varieties have been recorded by Carter, Brady, etc. I have also met with many white 

 specimens from many different localities, but it appears to me that the white specimens 

 are in all cases "dead" corals and that the whiteness is due to post-mortem discolouration. 

 In the genus Sporadotrema on the other hand there is a great range of colour. Yellow, 

 orange, pale pink, red and deep red specimens being known. My own view is that 

 differences in colour, unless associated with differences in form or structure are untrust- 

 worthy guides for the separation either of species or facies. 



The well known example of Melitodes chamceleon should serve as a warning to 

 those inclined to put their trust in colour. But when colour is associated with form 

 and structure it may be used as a valuable supplementary character. 



Of the genus Sporadotrema I recognise two species, S. eylindricum (Carter) which 

 is fully dealt with in this paper and S. mesentericum (Carter). 



Sporadotrema eylindricum may be conveniently divided into three facies. 



Facies Providentipe. This is a very robust form of great size, the largest specimens 

 being 27 mm. in height, with short branches, yellow to orange in colour, with a very 

 thick outer wall on the stalk and with the chamber outlines obliterated except at the 

 extremities of the branches (Plate 30, fig. 3). 



Facies Amirantise. This is a more delicate form, with longer branches than in 

 "Providentise," red or orange in colour with the outlines of the chambers well marked 

 on the branches and sometimes on the upper part of the stalk (Plate 30, figs. 6, 7). 



Facies Saya de Malhensis. This is a more delicate form even than "Amirantiae" 

 with longer and more cylindrical branches, pale pink in colour with the outlines of 

 the chambers usually well marked on the branches, but with the stalk usually remarkably 

 smooth and almost porcellanous in texture (Plate 30, fig. 4). 



There can be no doubt that intermediate forms will be found between these facies 

 but at present the facies Providentise is very well defined, the other two being more 

 difficult to distinguish. 



Sporadotrema mesentericum (Carter), Plate 30, fig. 5, Plate 31, figs. 11 and 12. 

 Syn. Polytrema mesentericum Carter (5). 



This species was described from a single water-worn specimen now in the British 

 Museum. Carter remarked at the end of his description that "when perfect" it "probably 

 resembled Polytrema eylindricum." 



Having found in a collection of Alcyonaria made by Professor Haddon in Torres 

 Straits several perfect specimens of this species preserved in spirit, I can confirm Carter's 

 opinion in so far as to include it with his species P. eylindricum in the new genus 



