108 COELENTERATA— ANTHOZOA phylum ii 



Astreopora Blv. Massive coralla. Coenenchyma porous and on upper 

 surface echinulate. Septa of dissimilar proportions ; columella and pali 

 absent. Tertiary and Recent. 



Dendracis E. and H, ; Cryptaxis Reuss. Tertiary. 



Turbinaria Oken (Gemmipora Blv,). Corallum foliaceous. Coenenchyma 

 tolerably compact and finely echinulate. Septa of similar proportions : 

 columella spongy. Cretaceous to Recent. 



Range and Distribution of the Hexacoralla. 



The group Aporosa of the Hexacoralla begins as the Tetracoralla disappear, 

 and develop a great variety of forms in the Trias, from the Mesozoic onward 

 to the present day they have continued to play a leading part in the con- 

 struction of coral-reefs. Of the f amilies constituting the Aporosa, the 

 " Astraeidae " is by all odds the most important and most protean, in com- 



parison to which the Fungida, Stylo- 

 phoridae, Pocilloporidae, Oculinidae and 

 Turhinolidae fall into greatly subordinate 

 rank. The other f amilies are all younger 

 than the "^s/raßw/ae/'not beginninguntil 

 the Jurassic, the Pocilloporidae, indeed, not 

 until the Tertiary. 

 Fig. 172. The Eupsammidae and Poritidae of 



Jcroporo ajifirZica (Duncan). Oligocene; Brocken- the Perforata OCCUr Sporadicallv in the 

 hurst, England, a, Calices enlarged ; b, Longi- ^-i • t r~i ^ -r ^ •^ -. • 



tudinal section, greatly enlarged. bllurian and üarboniterOUS, whllc it IS UOt 



until the Trias that the Anabraciidae and 

 Poritidae develop a large variety of forms ; from the Trias to the Tertiary, 

 however, these genera continue to be important reef-builders. The Eupsam- 

 midae attain their greatest development in the Tertiary and Recent, while the 

 Acroporidae belong almost exclusively to the present period. 



Occasional isolated deep-sea forms are met with in most of the several 

 geological periods, but the usual mode of occurrence of the Hexacoralla is 

 associated in masses in coral limestones ; the limestones may be of very vari- 

 able thicknesses, but as a rule are interstratified between deposits of distinctly 

 littoral character. Ancient coral-reefs most nearly resemble modern fringing 

 or barrier reefs, but not atolls, the origin of which is clearly dependent upon 

 peculiar conditions. 



The St. Cassian, Zlambach and Rhaetic beds of the Alpine Trias contain 

 large numbers of reef-building Hexacoralla; but the pure limestones and 

 dolomites of the Alps, as well as the Trias outside the Alpine region, are 

 frequently either almost or entirely destitute of coral remains. 



In the Lias, coral-reefs have been found in England, Luxemburg and 

 Lorraine. Certain beds of the Dogger, usually of but meagre thickness, are 

 occasionally charged with corals, as in Swabia, the Rhine Valley in Baden, the 

 Swiss Jura, Normandy and England. Coral limestones are abundantly 

 developed in the Upper Jurassic of the Jura Mountains in France and Switzer- 

 land, in Lorraine, Southern Baden, Swabia (Nattheim, Blaubeuern), Bavaria 

 (Kelheim), many places in France and England, as well as in the whole province 

 of the Alps, Carpathians, Cevennes and Apennines ; here the uppermost 



