MADREPORARIAN CORALS 55 



in the genera Meandrina, Coeloria, and the closely related 

 genus Leptoria. 



Meandrina. — In Meandrina the calices are principally 

 represented by long sinuous valleys, but in places more 

 circumscribed calices may be found. Between the valleys 

 there are ridges representing the fused walls of the calices, 

 for in these genera there is no peritheca as there is in Dicho- 

 coenia. There are numerous close-set septa and a median 

 spongy columella. The general appearance of the surface 

 of one of these Brain corals, as they are seen in a museum, 

 with all the soft fleshy parts removed, is that of a labyrinth 

 or maze of valleys without any regularity or order in their 

 arrangement ; and, if a single valley is traced for any 

 distance and found to divide into two valleys or to run into 

 another valley, it is difiicult to believe that they are essenti- 

 ally the same thing as, or, to use the scientific phrase, 

 morphologically homologous with, the calcareous cups that 

 support the well-defined polyps of such a coral as Galaxea. 



The series of intermediate forms which have been de- 

 scribed suggests that it must be so ; but the evidence would 

 not be complete without some knowledge of the characters 

 of the animals that construct them. 



In a living Brain coral the valleys are covered by a 

 continuous lamina of soft fleshy substance rising a few 

 millimetres above the hard coral substance, and this lamina 

 is perforated at intervals of 2 or 3 mm. by a number of 

 slit-like holes, the polyp mouths. The lamina rises on each 

 side to the ridge which is provided on both sides with two 

 rows of short stumpy tentacles. 



The colour of the living expanded polyps of the Brain 

 corals is often very vivid and brilliant. The oral lamina is 

 bright green with the mouths outlined in brown. The 

 tentacles are sienna-brown, becoming paler as they are ex- 

 tended in full expansion in search of food. When the polyps 

 are contracted, however, the green colour is lost owing to 

 the tentacles folding over the lamina, and the whole coral 

 seems to be covered by a darkish brown slime. There is a 

 great deal of variation in the shades and tones of colour in 

 these as in other corals ; and it is interesting that the notes 



