DISTBIBUTIOK OB COEALS. 245 



interpretation here given of the abyssal fauna is a valid one. In- 

 deed, it might be doubted altogether whether there is such a thing 

 as a true fauna of darkness; or, if existing, it may be considered 

 questionable whether the members composing it have not become 

 habituated to present conditions through force of accident or a 

 process of degeneration, rather than through selection as guided by 

 individual instinct or volition. It appears highly improbable on its 

 face that animals so feebly endowed with perceptive powers as 

 these appear to be, and which at the same time possess a most 

 extraordinary adaptability to extreme conditions of temperature and 

 pressure, should be so constituted in their relations to illumination 

 as not to be able to endure the quantum of light which passes 

 through even the shallowest stratum of water. 



The present broad distribution of the deep-sea Madreporaria 

 appears, likewise, to have obtained in the earlier geological periods. 

 Thus, Professor Duncan has shown, from his researches on the fossil 

 coral fauna of the West India islands, that a number of the forms 

 occurring there, in both the Eocene and Miocene formations, are 

 such as had been already previously described from the equivalent 

 deposits of Europe, e. g., Paracyathus crassus, Trochocyathus cor- 

 nucopise, T. laterospinosus, Ceratotrochus duodecimcostatus, the last 

 three from Italy, and the second also from the Vienna basin. Pla- 

 bellum appendiculatum, from the Oligocene beds of the island of 

 St. Bartholomew, is a species from Biarritz and Ronca; Trocho- 

 smilia subcurvata, from the same island, occurs in the Eocene beds 

 of Oberburg, in Styria, and T. arguta, at Castel Gomberto, in 

 Venetia, and other Oligocene localities." Other Tertiary species 

 have since been identified as being trans-Atlantic, and, doubtless, 

 many forms will be found whose range is still very much greater. 

 The Italian Conotrochus typus, Balanophyllia cylindrica, and Delto- 

 cyathus ItaUcus, are found also in the Australian Tertiary strata. "" 

 In view of the very extended range of so many of the species, the 

 distinctness of the Indian (Sindh) coral fauna, which holds scarcely 

 any species in common with any distant region, at least as far as 

 has yet been determined, is not a little remarkable. Considering 

 the apparent independence of the animals of this class, of the vary- 

 ing conditions of temperature and pressure which a habitation of 

 the deep-sea presents, and not unlikely also of other physical 

 conditions as well, it is difficult to account for the comparatively 



