446 PERCY SLADEN TRUST EXPEDITION 



same species is difficult to understand when the descriptions given by the two authors are 

 compared. 



Carpenter for instance lays stress on the fact that "the surface is always areolated" 

 and " the areolas are porous while their boundaries are composed of solid shell substance." 

 In describing the internal structure he says that the chambers communicate by large 

 circular pores and smaller orifices. It is noteworthy that he does not state that the walls 

 of the chambers are perforated by foramina nor in the figure does he show any foramina 

 except those at the surface. Carpenter's statement moreover that " sometimes its stalk, 

 instead of branching swells into a globular protuberance " is quite consistent with the view 

 that the form he described was a Homotrema. I have not seen any specimens of Polytrema 

 for which this statement of the shape could be considered accurate*. 



If Max Schultze's account of Polytrema be compared with that of Carpenter it will 

 be noticed that on all these important points the two authors are at variance. 



Carter (3) evidently examined a large number of specimens which he considered to be 

 Polytrema miniaceum from the Mediterranean Sea and from other parts of the world. 



His figure 6 of the species appears to me a composite production, the upper part 

 being taken from a true Polytrema and the lower part from a Homotrema. I have never 

 seen any such combination of the characters of the two genera in any one specimen. Both 

 his figures and his description appear to have been composed from notes taken from 

 the examination of a number of specimens of a mixed collection of the two genera. 



The very careful and accurate description of Polytrema by Merkel gives absolutely 

 no support to Carter's views. 



The coral may be in the form of flat encrusting disks, or of a short erect coralline 

 structure rising from a flat and sometimes spreading base and showing an expanded crown 

 springing from a constricted stalk terminating in a number of short arms or verruca? 

 (Plate 30, fig. 2, Plate 31, fig. 9). The size of the erect forms in my collection is from 

 5 6*5 mm. in height, 4 — 6 mm. in diameter across the crown, and 2 — 3 mm. in diameter 

 across the stalk. The specimens of flat encrusting forms that I have seen are (l) from 

 S. America 12 x 7 mm. and 8x8 mm.; (2) from Coin, Peros Banhos Atoll 6x8 mm. and 

 6x6 mm. The colour is nearly always red, but the tone of colour is darker and more 

 purplish than is usually the case in Polytrema t 



One series of specimens from Coin, Peros Banhos Atoll, was pink, and I have seen 



.Pallas, p. „52, wrote " Americana varietas plerumque verrucas magna? insequalis speciem habet, quae 

 superficie sparsos ramulos exserit." This is remarkable because it would apply admirably to many specimens of 

 Homotrema in my collection but not to any specimens of Polytrema, and at present there is not any evidence 

 that the genus Polytrema occurs on the American coast although Homotrema is common. 



t Note on colour. As it is very difficult to express in words the exact difference in colour between these 

 "red" corals I have consulted Mr H. Cadness of the Manchester Municipal School of Art and the suggestion he 

 makes is that the term "apricot red" might apply to the specimens of Polytrema from the Mediterranean Sea 

 and " salmon-colour " to the specimens from the West Indies. It is of considerable interest, in this connection, 

 to note that Pallas in his description of Millepora miniacea records his observation of a difference in colour 

 between his specimens from the Mediterranean and those from the American sea, the former being in all 

 probability specimens of Polytrema and the latter of Homotrema,. His words are, " Color hujus elegantissimi 

 Corallioli ex Mari Mediterraneo allati, pallide roseus solet, interdum saturatior. Quod in Coralliis Indicis 

 repentur pulchre cinnabarinum colorem exhibet, saturatissimum vero specimina in Coralliis testisque exesis 

 Maris Americani reperiunda." 



