COELENTERA — CORALS. 



51 



general Zoantharian type, and are in multiples of 6. In Gallery X. 

 many Palaeozoic corals they are in multiples of 4. The 

 former have therefore been called Hexacoralla, and the 

 latter, Tetracoralla. The wall of the Tetracoralla is often 

 wrinkled, so that they have also been called Rugosa. 



Owing to the difficulties of classification, all the fossil Table-cases 

 Anthozoa are placed together and arranged under the chief waU-eases 

 stratigraphical divisions, the British and foreign specimens i-6. 

 being separated as usual. 



Beginning with the oldest, we find Ordovician corals Table-case 

 from the Llandeilo rocks of North Wales and the Stinchar ^• 

 Limestone of Scotland. Streptelasma belongs to the Zaphren- 

 tidae ; Lyopora is allied to Favosites. These fossils are 

 ill-preserved, and the genera will be better studied later. 



The British Silurian corals are mainly from the Wen- Table-case 

 lock Limestone. Eirst come a number of genera placed in ^' 

 the family Favositidae, though not all with equal reason. 

 Favosites, the honey-comb coral, itself consists of five- or six- 

 sided tubes, set closely together ; each tube is divided by 

 flat tabulae, and its cavity is in connection with that of its 

 neighbours by small pores in the wall. Syringolites, a N'orth 

 American genus of the same age, has a similar structure, 

 but its tabulae are funnel-shaped (Fig. 20). Some regard 



Fig. 20. — A Favositid Coral, Syringolites huronensis, from the Silurian of 

 North America, a, a fragment of a colony, natural size, b, a single 

 calyx enlarged 8 diameters ; the tabula bears tubercles in radiating lines, 

 like the beginnings of septa, and is sharply bent downwards near the 

 centre, c, a single tube split longitudinally and enlarged 6 diam. ; 

 shows the funnel-shaped tabulae, d, a single tube seen from the 

 outside and enlarged 6 diameters ; shows the mural pores that connect 

 the cavities of adjoining corallites. (After Hinde.) 



these genera as related to Alveopora, a modern perforate 

 madreporarian. Others compare them with Syringopora, 

 also shown in the Silurian series, but better studied in its 



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