CALCAREOUS ALGAE OF THE MIDDLE EAST g 



their help and encouragement, and their very real interest in the project. Also my 

 thanks go to my fellow-students with whom I have had many interesting discussions, 

 and to the staff of the Sedimentological Laboratory for services of all kinds. 



Finally, I would acknowledge my indebtedness to the Management of Iraq 

 Petroleum Company, Ltd., who generously agreed to and made possible this liaison 

 between academic and economic geology. Dr. C. Thiebaud, Exploration Manager, 

 and Mr. H. V. Dunnington, Chief Geologist, who approved and submitted the project, 

 I thank sincerely and gratefully for their efforts on my behalf. All the material in 

 this paper has been presented to the British Museum (Natural History). 



II. STUDY AND CLASSIFICATION OF FOSSIL DASYCLAD ALGAE 



Modern views on the botanical classification of dasyclad algae, their relationship 

 to other green algae and the precise systematic status to be accorded them, may be 

 found in Fritsch (1935) and more recently in Egerod (1952) . Such work is necessarily 

 based on the detailed study of structure, development and reproduction in the living 

 plant. All the fossil forms described in this work are referred to a single family, the 

 Dasycladaceae. Within this family the subclassification into tribes has been largely 

 the work of palaeontologists, especially J. Pia, since the fossil forms are so numerous. 

 Pia's classification appeared in the 1920s (Pia 1920 ; 1927) and was followed with 

 slight modification and comment by later workers including Emberger (1944), 

 Johnson (1954a ; 1961b) and Kamptner (1958). 



Whilst it cannot be over-emphasized that as a general rule the fullest understand- 

 ing of fossils is only to be obtained from an understanding of their living descendants, 

 where skeletal structures can be studied functioning with the associated organic 

 tissues missing in the fossil, yet much depends on how much is preserved in the latter, 

 and how well it is preserved. In Recent members of the red algal family Chaetan- 

 giaceae, it was concluded by Svedelius (1953) that experimental spore-culture was 

 necessary for conclusive pairing of the morphologically distinctive sexual and non- 

 sexual generations. A morphological classification is thus inevitable with the fossil 

 Chaetangiaceae, which in addition are notoriously fragmentary. For this general 

 reason the account of dasyclad structure set out below stresses those structures and 

 features of the plant which are of assistance in an understanding of the calcified 

 remains found fossil. 



Individual living dasyclads are usually small, vertically-growing algae : one 

 observer described them as resembling " little green sausages " (Church 1895). 

 Attached at the base by a rhizoid or holdfast, the core of the plant is a proportionally 

 long cylindrical stem-cell, extending from rhizoid to apex. From this, whorls or 

 verticils of lateral branches are given off at successive closely-set levels : these 

 branches may themselves divide more than once, and they also bear the sporangial 

 bodies. Much of the plant above the rhizoid is crusted with calcium carbonate. 



The commonest fossils of dasyclads are thus small calcareous hollow cylinders with 

 tubular pores and cavities in the thickness of the wall, the pattern of pores and 

 cavities occurring again and again at successive levels in the wall-thickness along the 

 cylinder. The main central tunnel represents the stem-cell, the branching tubular 



