WEST AFRICAN COAST PORITES. 25 



GEOGRAPHICAL ARRANGEMENT OF 

 THE ATLANTIC AND WEST INDIAN PORITES. 



Group I,— WEST AFRICAN COAST AND CAPE VERDE ISLANDS. 



We begin the systematic review of the West African specimens with a brief notice of the 

 only known form which occurs where the Indo-Pacific and the Atlantic regions meet {P. Cape 

 of Good Hope 1). A description without a figure was given in Vol. V., p. 231, and it was there 

 pointed out that the form was probably found in False Bay, that is on the east side of the Cape 

 point, where the temperature of the water is several degrees higher than on the Atlantic or west 

 side. It is here figured (PI. I. fig. 1), because it illustrates at a glance the difference in habit 

 between the Indo-Pacific and the Atlantic forms, which has been referred to lq the morphological 

 section, pp. 12 and 13. On the other hand, the fact that this form illustrates the Indo-Pacific 

 type helps to justify our having regarded it as l)elonging to this latter and not to the Atlantic 

 group. Further, inasmuch as the growth forms of the specimens are thick, encrusting cakes, we 

 might have concluded that, had they been Atlantic forms, they would have shown some approach 

 to the Astrffioid * hal)it. We find, on the contrary, that their skeletons are built up of compara- 

 tively thin delicate trabecule closely packed, and rising to form thin walls and pali, of which 

 latter only the four lateral principals are at all conspicuous. There can Ije no doubt, then, that 

 this form belongs to the Indo-Pacific group, though it occurs on the border line between the 

 two regions. It shows no trace of transitional characters, although it is perhaps only right to 

 add that if it did it is doubtful whether we should have been able to recognise them in such 

 an intricate and subtile morphological complex as the Pwitcs skeleton. 



1, Porites West Africa 1. (P. Africana Occidentalis prima.) 

 [The Gaboon ; Paris Museum.] 



Description. — The corallum is very thin and encrusting, with edges under 1 mm. thick, 

 and supported by stout wrinkled epithecse. 



The calicles are small, the larger about 1 mm. in diameter, angular, and flush with the 

 surface. The walls consist of thin, wavy, not zigzag, tkreads, which are sometimes flattened 



* On the use of this term in this Volume, see p. 142. 



