SYSTEMATIC AFFINITY OF ACROPORELLA ASSURBANIPALI 



113 



the variability oftlie species and some qualitative characters such as 

 the shape of thallus, laterals and reproductive organs would have 

 required more abundant material. 



The thallus is apparently cylindrical and simple. Primary laterals 

 are arranged in moderately close whorls. Their position between 

 whorls, alternated or in continuity, is not evident. However they are 

 phloiophorous and rather strong, almost perpendicular to the stem 

 axis. The transverse section of the primary pores is rectanglar in the 

 middle part and square in the distal part. The number of primary 

 laterals per whorl can be estimated as 1 1 -1 2. This value corresponds 

 well with that supplied by Elliott. 



Two strong secondary laterals originate from the distal end of each 

 primary lateral. They show a subcylindrical inner part of modest 

 length, 0.1 1-0. 12 mm, and 0.10-0.12 mm in diameter, followed by 

 a part that flares out quickly, so making a cortex at their distal end 

 (pl.l, fig. 3). The two secondary laterals are nearly placed on an 

 horizontal plane, i. e. parallel to the verticillar plane. 



Elliott did not identify the twofold laterals, but he interpreted the 

 shape of primary and secondary laterals in longitudinal section as 

 parts of a single lateral. He correctly described the first inner part 

 (primary) as 'a fig- or flask-shaped cavity', and the second outer part 

 (secondary lateral) as 'a slightly curved tube'. 



The holotype occasionally shows structures referable to reproduc- 

 tive organs (ampullae: pi. 1 , fig. 2). The ampulla is set at the distal end 

 of each primary lateral, over the plane where the secondary laterals 

 are placed. It is of spherical shape, 0. 1 1 mm in diameter, joined to the 

 primary lateral probably by means of a short peduncle. The difficulty 

 in observing the reproductive organs can be explained by the fact that 

 most of them were empty and were destroyed after the re-crystallisa- 

 tion of the aragonitic calcareous skeleton. Only those filled by matrix 

 have a chance of being preserved and recognised in thin section. 



The calcification consists of a strong calcareous skeleton. It 

 envelopes the primary laterals, the ampullae and the secondary 

 laterals up to their swollen distal end conesponding to the inner edge 

 of the cortex. The smooth and regular inner cavity indicates 'hat 

 calcification probably reached the wall of the central stem. More- 

 over, in this area the primary laterals open with a reduced pore. 



The main biometrical values of the alga are given in Table 1 . 



PALAEONTOLOGICAL RECONSTRUCTION 



The reconstruction in Figs. 2 and 3 takes into account the biometrical 

 values and the morphological characters previously given. The 

 number of pores in a whorl has been chosen to be twelve, and a cortex 

 of hexagonal meshes set horizontally has been supposed. The latter 

 seems to be the most likely arrangement for that number of pores in 

 a whorl and the distance between whorls. 



Considering the apex of the thallus, no elements can be deduced 

 from the single specimen at our disposal, and therefore it has been 

 drawn by inference from extant species of Neomeris (e.g.. N. 

 anmdata). 



TAXONOMIC ATTRIBUTION 



The species is attributed to the genus Neomeris from the evidence of 

 primary laterals in verticils that bear distally two secondary laterals 

 and an ampulla. The fact that the species exhibits two secondary 

 laterals arranged in an horizontal plane beneath an ampulla, allows 

 us to refer M assurbanipali to the subgenus Lanaria. The species, if 

 compared with others of the same genus, shows such a combination 



Fig. 3 Neomeris (Larvaria) assurbanipali Elliott nov. comb. Transverse 

 reconstruction of the thallus. Upper half: part of a verticil showing the 

 central siphon, primary laterals, secondary laterals and ampullae without 

 calcification. Lower half, right: transversal section through the primary 

 and secondary laterals, calcification in black. Lower half, left: 

 transversal section through the primary laterals and ampullae, 

 calcification in black ( x 45). 



of characters as to maintain the taxonomical validity. In addition 

 Neomeris (Larvaria) assurbanipali differs strikingly from all the 

 other counterparts by having a calcareous skeleton that envelops the 

 primary laterals entirely, and seemingly reaches the central stem. 



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