CALCAREOUS ALGAE OF THE MIDDLE EAST 41 



Formation (Maestrichtian level) of Murban No. 53 well, Abu Dhabi, Arabia. V. 

 52652. 



Syntype. The specimen figured in pi. 9, fig. 3, same locality and horizon as for 

 holotype. V. 52653. 



Other Material. Several incomplete random thin-sections, provenance as 

 above. 



Remarks. This remarkable species does not at first sight appear to show the 

 branch-structure of the genus Cymopolia. The large and conspicuous swollen 

 primaries suggest a typically cladospore Mesozoic genus. However the small 

 terminal cymopoliform branch-systems are distinctive. They are typically choristo- 

 spore, and lead to the conclusion that the species shows one possible transition 

 between cladospore and choristospore organization. Typical C. tibetica of the same 

 geological age show expanded primaries, but to a very much less degree, and this 

 feature survives not uncommonly in the Tertiary subgenus Karreria, and even 

 occasionally in specimens of living Cymopolia (see remarks above under C. tibetica). 

 In these later forms this character is best regarded as vestigial. 



C. eochoristosporica appears to show the cladospore/choristospore transition by the 

 appearance of a small choristospore development superimposed on the large clado- 

 spore branch, presumably with partial transference of sporangial contents. In this 

 connection it is as remarkable an evolutionary record as Pia's suggested interpreta- 

 tion of his forms trichophora and vesiculifera of the Triassic Diplopora annulata as 

 endospore and early cladospore respectively. Here the transition from endospore to 

 cladospore is similarly considered to have taken place within the one species, but the 

 separate characters are shown in different individuals with a possible geographical- 

 environmental distribution of the two forms. The scarcity of my Maestrichtian 

 Cymopolia spp., when compared with Pia's abundant Triassic diplopores, precludes 

 an investigation of this possible subsidiary parallel for the present. Moreover, 

 Herak's review of Pia's work on this subject (Pia 1920 ; Herak 1957), whilst clearing 

 the taxonomic confusion involved, also shows the many uncertainties which attend 

 evaluation of the Triassic species in its varied forms and occurrences, even with an 

 abundance of material for study. 



For these reasons the limited material now studied is described as a new species, 

 the available individuals showing clearly in their morphology the characters on which 

 the species is based. 



Cymopolia tibetica Morellet 



(PI. 8, figs. 3, 4) 



1916 Cymopolia tibetica Morellet : 47, pi. 15, fig. 10, text-figs. 14-21. 



1927 Karreria tibetica (Morellet) Pia : 83. 



1940 Cymopolia tibetica Morellet ; Pfender : 234. 



i960 Cymopolia tibetica Morellet ; Elliott : 223. 



Description (summarized from Morellet) . Cymopolia with rather straight-sided 

 cylindrical units of up to 2-5 mm. long and diameters from i-i to 1-5 mm., diameter of 



