The Relationship of the Tetracoralla to the Hexacoralla. 187 



Permian.— Th^ fate of these stocks in the cold waters result- 

 'ing from the early Permian glaciation can only be conjectured. 

 Their latest recorded occurrence is in the Permian of the great 

 medial sea Tethys, where the individuals are common and appar- 

 ently are confined chiefly to the Asiatic area. Polycoclia is the 

 single well defined genus of the western and northern Permian 

 sea of Zechstein time in western Europe and England. Accord- 

 ing to Waagen Lonsdaleia and Ample xus are found in the Permo- 

 Carboniferous beds of the Salt Range of India and Zaphrentis, 

 Clisiophyllum, {?) Dihunophyllum, and Pterophyllum have been 

 reported from the Chitichun of the central Himalayas. The 

 j restricted number of genera in these localities can only in part 

 f be accounted for by the lack of adequate preservation, for reef- 

 I building forms occur abundantly. Other forms occur in Aus- 

 tralia and New Zealand. This fact shows that in what appears 

 to be their last stronghold, Tethys, the Tetracoralla were losing 

 ground in point of numbers of genera, and that this decline 

 was far more advanced in the cooler western and northern 

 waters than in those of the eastern medial region. With regard 

 to later occurrences, the evidence appears to be in favor of an 

 earlier abimdance of Triassic forms in western than in eastern 

 Tethys, for it is the Alpine region in which the new forms first 

 attain a vigorous reef-building character. The great gap in 

 the record of coral evolution therefore comprises all late Permian 

 and early Triassic time, and this absence of material does not 

 permit a study of the evolutional relations of these stocks, but 

 it is certain that in the Middle Triassic the new forms, now 

 Hexacorals, were conspicuous in the West, while it was not 

 until the Jurassic that they appeared in large numbers in the 

 East. This fact is suggestive rather than demonstrative of a 

 western Tethyian origin for the Hexacoralla. 



