174 



THALLOPHYTA. 



[CH. 



Diplopora. Fig. 85, A and B. 



This genus of algae is characteristic of Triassic rocks, and is 

 especially abundant in Muschelkalk and Lower Keuper lime- 

 stones of the Alps, Silesia, and elsewhere. The thallus, or 

 rather the calcareous portion of the thallus, has the form of a 

 thick-walled tube, with a diameter of about 4 mm., and 

 occasionally reaching a length of 50 mm. At one end the 

 tube has a rounded and closed termination, and the wall is 

 pierced throughout its whole length by regular whorls of fine 

 canals. Diplopora agrees with Cymopolia in its main features. 



Fig. 35, A, affords a diagrammatic view of a Diplopora tube, 

 and shews the arrangement of the numerous whorls of canals. 

 In fig. 35, B, a piece of limestone is represented containing 

 several Diploporas cut across transversely and more or less 



Fig. 35. A, B, Diplopora. x 2. C, D, Gijrojjorella {sifter Benecke. x4). E, Cal- 

 careous segments of Penicillus, from a specimen in the British Museum. 

 X 5. F, a single segment of Ovulites margaritula Lam. x 4. G, Confervites 

 chantransioides Born, (after Bornemann. x 150). 



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