FORAMINIFERAN AND OTHER CORALS i8i 



encrusting discs on corals or shells, which may or may not 

 show the scars of the broken-off stems. Specimens of this 

 kind can frequently be found on the dead branches of other 

 corals or on shells from tropical waters of the Indian and 

 Pacific Oceans. 



HoMOTREMA. — Until quite recently the genus Homo- 

 trema has been confused with Polytrema on account of its 

 size, colour, and habit, but a detailed study of its structure 

 proves that the two genera are quite distinct. 



If corals and shells from the reefs of the West Indies 

 be examined they will frequently be found to bear little 

 red spots and discs very similar to the spots and discs of 

 Polytrema found on corals and shells from the Mediterranean 

 Sea and the East Indies, and some of them may support 

 short knobbed processes something like a 

 minute pollarded willow tree (Fig. 89). 



Pallas seems to have noticed two of 

 the characters which distinguish Homo- 

 trema from Polytrema, for he says that 

 the specimens from American seas are of 

 a darker red colour than those from the 

 Mediterranean Sea, and that they have 



. -^ Fig. 89. — Homotrema 



the form of large irregular warts from rubnim. :< 2 diams. 

 the surface of which a few short branches 

 spring.^ But Pallas did not feel justified in separating the 

 two varieties, and included them both in his species Mille- 

 pora miniacea. 



The characters that separate Homotrema from Poly- 

 trema may be summarised as follows : The form may be 

 that of a simple encrusting disc, but, when standing erect 

 from a spreading base, of the shape of a wart or knob with 

 sometimes a few very short projections at the free extremity. 

 The surface is mapped out into areas which are slightly 



^ " Color hujus elegantissimi Corallioli ex mari Mediterraneo allati, 

 pallide roseus esse solet, interdum saturatior. Quod in coralliis Indicis 

 reperitur pulchre cinnabarinum colorem exhibet ; saturatissimum vero 

 specimina in Coralliis testisque exesis Maris Americani reperiunda. 

 Americana varietas plerumque verrucae magnae inequalis speciem habet, 

 quae superficie sparsos ramulos exserit." — Pallas, Elenchus Zoophytorum, 

 1766. 



