CALCAREOUS ALGAE OF THE MIDDLE EAST 29 



precedes the evolution of the choristospore structures with which the terminal discs 

 of Acetabulariae have been thought homologous. It therefore seems probable that 

 it represents an earlier development of similar morphology, but from a different 

 source. This point is more fully discussed below under dasyclad evolution (p. 99). 

 In the Middle East Clypeina is represented by species in the Upper Jurassic and 

 basal Cretaceous, and again in the older Tertiary (Palaeocene and Eocene). A 

 clypeiniform alga, still incompletely known, occurs in the Permian, and a Triassic 

 species is now known from elsewhere (Pantic 1965). The numerous species listed 

 throughout the Cretaceous succession in the western Mediterranean area (Algeria, 

 France, etc.) by Emberger (1957) have not been noted in Middle Eastern material 

 during the examination of thousands of thin-sections, often richly algal, and in fact 

 only three records occur for this portion of the geological column. 



Clypeina jurassica Favre 

 (PI. 3, figs. 2-5 ; PI. 4, figs. 4, 5, 6) 



1927 Clypeina jurassica Favre : 34, pi. 1, figs. 2, 3 ; text-figs. 10, 11. 



1932 Clypeina jurassica Favre ; J. Favre : 12, text-fig. 2. 



1951 Clypeina jurassica Favre ; J. Morellet : 399, pi. 22. 



1955b Clypeina jurassica Favre and C. hanabatensis Yabe & Toyama ; Elliott : 125. 



1958a Clypeina jurassica Favre ; Donze : 21. 



1962 Clypeina jurassica Favre ; Powers : 131. 



Description (from Middle Eastern material). Discs (fertile verticils), saucer to 

 open-funnel shaped, diameter up to 2-4 mm., height up to 0-75 mm. composed of up 

 to 24 fused radiating tubules (sporangial elements) around a central cavity of up to 

 0-5 mm. ; the majority of normal specimens are about 2-0 mm. diameter, with 18-20 

 tubules and central cavity of about 0-4 mm. The tubules widen slowly outwards, 

 and the outer ends are open : on the external surfaces, upper and lower, the tubules 

 are demarcated by shallow grooves. Although in normal specimens the tubules are 

 nearly circular in cross-section, they tend to vary according to the size of the disc of 

 which they form part, and in the larger examples, with more numerous tubules, the 

 tubule cross-section shows the height greater than the diameter. The tubules fuse 

 to form a conspicuous thickened central basal ring on the lower surface of the disc : 

 this is most developed in the funnel-shaped examples. In a large example of 

 estimated 2-5 mm. disc-diameter or more, the inner diameter of a single tubule 

 increases from 0-130 mm. near the centre to 0-390 mm. in 1 mm. tubule-length : 

 the diameter of the single inner communicating pore between central cavity (stem- 

 cell) and tubule is 0-050 mm. ; and the single wall-thickness about the middle of the 

 tubule is 0-065 mm - I n random thin-section the united walls, back to back, of any 

 two adjacent tubules show as radial fibrous calcite, clear or yellow, separated by a 

 dark fine, and in horizontal (transverse) sections these median structures project 

 radially at the margin, to give a torn serrated appearance to the whole disc. This 

 wall-structure and the open ends of the tubules, whatever their significance in terms 

 of the original plant-calcification or subsequent diagenesis, are characteristic of the 



