2 MADKEPOltARIA. 



locality, this is not the case with sessile forms as highly developed as the Corals. Whatever 

 the " species " of corals may be, we know nothing about them, and can know nothing about 

 them until we study them by means of experimental cultivation. We only know the local 

 forms. Hence local forms are the only available units with which we can do solid work. We 

 have to study them with a view to arranging them into larger groups extending over larger areas. 

 We are not, therefore, surprised to find that the forms inhabiting the Atlantic area have a 

 character of their oMm distinguishing them from those inhabiting the Indo-Pacific. We might 

 have assumed it, but as a matter of fact, its discovery was solely due to observation and 

 analysis. What these distinguishing features of the Atlantic forms are will be described below 

 in the morphological section, p. 12. 



It now seems probable that the forms of the Indo-Pacific region wUl ultimately have to be 

 divided into smaller groups corresponduig to definite areas : for instance, that the Eed Sea forms 

 will be found to have characters peculiarly their own. A dim perception of this was pointed 

 out by the author — but, as he now thinks, quite misunderstood — with regard to the genus 

 Turhinaria (see Vol II., 1896, p. 18, last paragraph.) If this can be established generally, a 

 great reform in the classification of the Corals cannot be long delayed. All purely imaginary 

 groups such as species or morphological " forms " of indefinite distribution will be abandoned as 

 units, and the Corals will have to be treated as we treat the races of men — as factors in the areas 

 which they inhabit, and upon the conditions of which they largely depend for their peculiarities. 



In connection with this fact that the forms to be dealt with in this Volume show structural 

 peculiarities, distingiushing them from the Indo-Pacific forms, we may point out that the 

 Atlantic area is now for all practical purposes, that is so far as Porites is concerned, quite 

 separated from the Indo-Pacific, and has been thus separated for an indefinite period. It is 

 true that Porites creep down the east coast of Africa apparently in isolated specimens beyond 

 the limit of coral reefs. For instance, one such is found at the Cape of Good Hope (see p. 25), 

 but as we pass into the Atlantic round the Cape point the temperature of the water immediately 

 falls, apparently rendering the existence of Porites impossible. Certain it is that the first 

 isolated specimens known to occur on the Eastern shore of the Atlantic are found in the 

 Gaboon Estuary, nearly 2500 miles to the north of the Cape (see p. 25). If on the eastern side 

 of the Atlantic, the two Porites areas on the sides of the Cape of Good Hope, are separated by 

 conditions of temperature, the same is still more obviously the case at Cape Horn. The 

 most southerly Porites so far known on the Pacific shores of South America occurs in the Bay of 

 Panama, on the Atlantic side on the AbroUios reefs, south of Porto Seguro, nearly 3500 miles 

 north of Cape Horn. Further research is certain to reveal Pacific forms much further south 

 than the Bay of Panama, but there is no chance whatever with the known temperature condi- 

 tions at the Straits of Magellan that the Pacific and Atlantic Porites faunas meet, or have 

 met, within recent geological periods. 



No connection between the Pacific and Atlantic oceans seems to have existed across the 

 Isthmus of Panama since the early Miocene or possibly since the OUgocene.* But on the 



• Cf. Professor Gregory, Quart. Journ. Gaol. Soc. li. (1895) p. 308. 



