CALCAREOUS ALGAE OF THE MIDDLE EAST 77 



by a wet membrane to give normally a lamellar structure, whatever the varied 

 microstructure (fibrous, prismatic, etc.). This difference in structure makes the 

 algal calcium carbonate much less resistant to diagenetic changes than that of almost 

 any other fossil, with frequent disastrous results familiar to the palaeontologist. 



Ignoring near-pure limestones in which the results of calcium carbonate solution- 

 replacement mechanisms are common, it is seen that in the marly facies in which 

 Hensonella (or S. dinarica) abounds the undoubted dasyclads such as Actinoporella, 

 Munieria and Cylindroporella and other species of Salpingoporella, show skeletal 

 remains preserved as white replacement calcite, coarsely crystalline in thin-section 

 under moderate magnification. This is interpreted as diagenetic replacement of 

 original aragonite. Hensonella stands out conspicuously by its translucent yellow 

 radially-fibrous structure. This structure represents a diagenetic alteration of 

 original calcite, not originally amorphous as in some other algae, and not of aragonite. 

 The radial structure is original, a point emphasized by compaction-fractured speci- 

 mens, and alteration has taken place in the wall-material between these partings, and 

 not to obliterate them. Only very rarely and incompletely has a later change 

 affected this resistant structure, and then not to the extent seen in associated 

 dasyclads. These undoubted dasyclads, sealed in the same matrix and subjected to 

 the same treatment, have behaved differently. 



The thin inner dark layer is also anomalous for a dasyclad. If, as suggested by 

 Edgell, it represents the thickened cell-wall of the stem-cell, then this is unusual in 

 living dasyclads and not seen in fossil forms. In Hensonella it is consistently present 

 under varied conditions of preservation from very different localities, which suggests 

 that it originates from an original feature of the organism, even if diagenetically 

 altered, and not from diagenesis itself. Moreover, although localized thickening of 

 the outer stem-cell wall is known in the living Dasycladus, there is no trace of this 

 preserved in the fossil Pagodaporella now considered related (see above, under 

 Pagodaporella), even though the former presence of the structure is inferred. 



In conclusion, I consider that this organism is best classified as a problematicum. 

 The original comparison with a scaphopod appears unlikely, but the wall-material is 

 not that of known dasyclads, and certainly not that of the associated dasyclads in 

 the same beds. 



Appendix. List of Middle East materials referred to Hensonella. 



In Iraq, Qamchuqa Formation (Barremian level) of Sarmord, and Sarmord 

 Formation (Barremian-Aptian level) of Sekhaniyan, both Sulemania Liwa ; sub- 

 surface Garagu Formation (Valanginian-Hauterivian) of Kirkuk no. 116 well 

 Bottom lower Cretaceous, probably Valanginian, at Haushi, South Oman, Arabia. 

 Common at Barremian-Aptian level in south-west Persia, and recorded from the 

 Aptian of Galilee, Israel (Reiss 1961). 



Genus TERQUEMELLA Munier-Chalmas 1877 



1877 Terquemella Munier-Chalmas : 817. 



1920 Terquemella bellovacina Munier-Chalmas ; Costantin : 1031-32. 



1922 Terquemella Munier-Chalmas ; Morellet : 18. 



