i.! CALCAREOUS ALGAE OF THE MIDDLE EAST 



Calcification 



During individual development recent dasyclads pass through several growth 

 stages : calcification begins fairly late, often being initiated around the early repro- 

 ductive structures, and thus it is the adult plant of which a fossil record is possible. 

 Occasionally exceptional fossils, such as the Cretaceous Trinocladus, show differences 

 in detail between the lower, earlier formed whorls and the upper, later ones, both 

 being calcified. However, a combination of capriciousness in degree and occurrence 

 of calcification for the members of the family viewed together, and constancy for the 

 calcification of the individual species, is the rule in the Dasycladaceae. 



Consequently, the reconstructions possible of the plants which originated the 

 calcareous fossils vary enormously. With heavy calcification a record is preserved 

 of the stem, branch and sporangial details, and also the outline of the whole plant, 

 only the finest branchlets projecting further during life. With those which calcify, 

 but come apart after death, a fair degree of reconstruction is possible, and chance 

 preservation of rare complete specimens illuminates the common segments or debris. 

 Where calcification is confined to a narrow zone, either close to the stem-cell as in 

 Pagodaporella, or between the tips of the branchlets only, as with Tersella, the 

 details of the plant will probably always be doubtful. Finally, such odd remains as 

 Aciculella, already mentioned, or tiny dissociated elements like Terquemella, render 

 necessary the description of form-genera whose components may be of diverse origin 

 and whose position within the family is unknown. 



List of Middle Eastern Fossil Dasycladaceae 



In the list below, those genera of dasycladaceae recognized in the course of the 

 present work are set out under the appropriate " tribes ", or subdivisions of the 

 family. These tribes, proposed by Pia (1920 ; 1927), have been followed and modi- 

 fied by later workers, notably in the comprehensive schemes of Emberger (1944) and 

 Kamptner (1958) while other workers, elements of whose classifications have been 

 especially considered here, are Morellet (1922), Johnson (1954a ; 1961b) and Rezak 



(1959a). 



Classification of this kind is based on structure as preserved in the fossils, and on 

 phylogeny, which may be regarded in this connection as interpreted structure. The 

 student of phylogeny assigns values to elements of structure in accordance with his 

 or her experience of the group studied. Close similarities and near-identity, 

 particularly of external form and gross structure, are often discounted in favour of 

 smaller and less obvious features. These latter are valued on account of their 

 persistence throughout time or their alleged significance as early or late manifesta- 

 tions of distinctive structures in related members of the group. In general, this 

 interpreted structure determines the taxonomic category allotted. However, the 

 success of a group, evidenced by numerical abundance of individuals and extensive 

 minor variation from a common structure, as opposed to rare, but profound deviation 

 which were evidently biologically unsuccessful or unfortunate, often leads to a 

 taxonomic up-grading of the group being classified. 



Such classification, with its very different allocation of importance to the same or 



