1867.] DUNCAN WEST-INDIAN CORALS. 15 



meet external conditions, and may have resolved itself into H. 

 cavernosa. 



The assemblage of Heliastrcece connects the Trinidad deposit with 

 the Nivaje shale of San Domingo and the Marl of Antigua, in a 

 palceontological sense, and indicates a reef in some form or other. 



Brachyphyllia, Eeuss, is a genus whose species are for the most 

 part of Gosau-chalk age ; but there is one f>ublished species from 

 the Miocene of Turin, and I have MS. notes of another form from 

 Bassano. The species now described are well marked, and must 

 suggest what has already been noticed* as regards the Coral-fauna 

 of San Domingo,^ Jamaica, and Antigua — the relation between the 

 Coral-fauna of the Hippurite-age and that of the Antillian Miocene. 



Isastrwa confusaf is the third species of Isastrcea of the West- 

 Indian Miocene, and is as aberrant as regards its septal arrangement 

 as the Triassic and Liassic species ; but this variation from the arti- 

 ficial type is to be expected in the oldest and youngest species of 

 every large genus. The variability of species, and their aberrant 

 forms in genera about to become extinct (that is to say, extinguished 

 in the perceptions of the zoologist), is very marked in the Madrepo- 

 raria, as it is in Echinodermata, Trilobita, and Pachydermata. 



Stylopliora raristella, Defrance, sp., is an abundant fossil ; and very 

 beautiful examples of the papillate coenenchyma between the calices 

 are very common. There is no coenenchyma in the young corallum, 

 but it appears with growth. The S. minuta is closely allied to the 

 S. rainstella, which is a characteristic Falunian coral. 



Porites astroides, Lamarck. This is a species whose individuals are 

 , very large, and doubtless formed large portions of old reefs, as they do 

 still in the present Caribbean sea. 



Taken as a whole, the eighteen species, which are all compound, 

 indicate vigorous coral-growth and the conditions most favourable 

 for the existence of a reef — that is to say, pure sea-water, the absence 

 of fresh water, a deep sea close at hand, and neighbouring high land 

 in an area of oscillation. 



These external conditions are not now in existence ; and Trinidad, 

 the southernmost of the West-Indian Islands, is too close to the 

 delta of the Orinoco and the estuaries of the Gulf of Paria for the 

 growth of the species of the West-Indian Coral-fauna. The Orinoco 

 effectually stops the passage of the West-Indian species to the south. 

 Formerly, when the great plains through which the Orinoco passes 

 were a Miocene sea- bottom, there may have been an open sea, as 

 large as the Caribbean, to the west and south, and the coral-reefs 

 would have been supported by the outliers of the mica-slate ranges 

 of Colombia. 



6. 2^he Mineralization of the Specimens. — The mineralization of 

 the St. Croix specimens is somewhat peculiar. A few are imbedded 



* Duncan and Wall, op. cit. 



t Since this written MM. Duchassaing and Miclielotti (in their "Supplement 

 au M6moire sur les Coralliaires des Antilles, Mem. Acad. Turin, 2^ serie, vol. xsiii.) 

 notice Dimorphastraa Guadalujpensis from the Tertiaries of Gruadeloupe; the 

 genus is of Gosau age. 



