CALCAREOUS ALGAE OF THE MIDDLE EAST 71 



Within the outer pored tube described above there occurs in a majority of speci- 

 mens a continuous solid dark calcareous layer, attached to the inner surface of the 

 outer mesh. In many specimens this layer is indistinguishable in colour and texture 

 from the dark outer calcite mesh, and has the appearance of being part of the tube ; 

 in some it shows as a lighter, obscurely banded layer of variable thickness, eccen- 

 trically placed with regard to the outer tube, i.e. much thicker on one side than on the 

 other in transverse section ; and sometimes it is absent. This layer is interpreted as 

 a secondary deposit formed subsequent to the death of the tube-building organism, 

 though not after burial, for occasional specimens show other organisms attached to 

 its inner surface. The reason for its occurrence is discussed above. Consideration 

 of the algal dust infillings described in Koninckopora by Wood (1943) did not permit 

 close comparison, but the observations of Johnson (1957 : 181) are of interest. The 

 lining layers in Pseudovermiporella may be of similar origin to the granular crystalline 

 calcite described by Johnson, and considered by him to have been formed probably 

 almost contemporaneously with deposition, whilst objects were movable on the 

 sea-floor. 



Within some but not all specimens there occurs an innermost tube of thin dark 

 imperforate calcite, roughly circular in cross section, and of considerably lesser 

 diameter than the inner diameter of the outer tube from mesh to mesh. Sometimes 

 this thin layer forms the inner boundary of the secondary layer mentioned above ; 

 sometimes it is seen " free " within the central cavity, filled with transparent calcite 

 and separated by the same mineral from the outer pored tube or from the dark 

 secondary lining calcite if present. When intact, it is not invariably central in 

 position ; not infrequently it is broken, and sometimes small organisms are seen 

 attached to it. It is considered to be of organic origin, and its relation to the outer 

 pored tube is discussed above. 



The smallest tubes show in section as bubble-like clusters, rather like the nucleo- 

 conchs of certain foraminifera. Although some of the sections in such a cluster are 

 a result of the plane of section cutting a meandriform tube more than once, it seems 

 likely that more than one individual, budding from a centre, may sometimes be 

 present. The walls of these tiny immature tubes are composed of the innermost thin 

 dark organic calcite just described ; only when they are larger does a pored outer 

 tube, with proportionally small pores, appear. There is considerable variation 

 between individuals in the diameter-size at which this occurs. 



In sections of the mesh of adult individuals, small bubble-like sections of the inner 

 layer of small, usually single individuals sometimes occur, suggesting attachment or 

 budding. Small pored tubes occur within the tubular cavities of larger individuals, 

 attached either to the inside of the main outer mesh (rarely to the secondary calcite 

 lining this, if present) ; or to the outside of the inner, thin-walled tube. They are 

 never found within the latter when it is unbroken. 



Horizon. Upper Permian of the Middle East. 



Material. Very numerous thin-sections from Permian limestone at Jebel Qamar, 

 Peninsular Oman, Arabia (foraminiferally dated as probably Upper Permian by 

 Dr. M. C. Chatton). Seen also in derived Permian material in Upper Cretaceous, 



