those species — for the most part solitary in habit — which do not help to form reefs. Now 

 this simple method of dealing with the matter may serve well enough for some latitudes, but 

 it wil! not answer for tropical latitudes where the temperature, even at a depth of a hundred 

 fathoms, is fairly high. 



For, at any rate in the Oriental region, everyone who has worked in the field knows 

 that, outside the zone of reef-forming corals, there are two separate coral faunas. One of these 

 is a characteristic local assemblage of small solitary species of Ettpsammidce \ Lophoseridce \ and 

 Tii,rbinolid(r, that flourish on shelly and shingly ground in depths of twenty to sixty fathoms 

 or thereabouts, where the water is still warm ; while the other includes a number of true cold- 

 water forms having decided afhnities with the corals living in the depths of the Xorth Atlantic 

 and with those that inhabited the Mediterranean basin in Tertiary times. 



These two assemblages of Madreporaria — the one of small tropical species that are 

 now invading the depths : the other of well-established abyssal species having a more northern, 

 or at any rate a more cosmopolitan, cast — are quite distinct, even though a few of the 

 deep-sea species, such for instance as Batkyactis, do occasionally find their way into shallow water. 



So far as the "Siboga" material is concerned, I have ventured, with Prof. Max Weber's 

 assent, to settle the matter by applying to the non-reef-forming corals the same measures that 

 have been found convenient for so many other groups of marine animals, and I have therefore 

 separated, as worthy of independant treatment with regard to questions of oceanography, all 

 those species that ordinarily live below the hundred-fathom line. 



These species are here collected under the name of Deep-sea Madreporaria. The remainder 

 of the collection I hope to deal with hereafter as "Solitary Madreporaria of the Prope-littoral Zone". 



The number of true deep-sea species included in the present instalment is 75, belonging 

 to 29 genera and subgenera and 5 families. 



Of the species that are sufficiently well preserved for determination 38 have never, to the 

 best of my belief, been previously described, except in a preliminary communication published 

 in the Journal of the Netherland Zoolcgical Society. 



Among these undescribed species there are a few for which new generic definitions have 

 had to be proposed. These new genera are (1) Lochiuccotroclius, which is essentially a Conotrochus 

 that forms small colonies by budding ; (2) Citharocyathus, which appears to show a line of 

 connexion between Deltocyathus and Nototrochus ; and (3) Placotrocliidcs, which seems to 

 connect Placotrochus and Platytrochus. 



Several of these deep-sea species, described as new, have however a very close resem- 

 blance to species, described by Seguenza, from the Sicilian and Calabrian Tertiary rocks, and may 

 perhaps prove to be identical with them. 



Several species that range across the Atlantic and into East Inclian waters, most of them 

 also occuring in a fossil state in the Tertiary Deposits of Southern Europe, are found amongst the 

 "Siboga" material, such as Deltocyathus italicus Michelotti, Desmophyllum cristagalli E. & H., 

 Flabcllum laciniatum Philippi (a variety), Amphihelia oculata Linnens and Amphihelia ramea Muller. 



