. Bulletin of the British Museum (Natural History) Geology Supplement. ORDOVICIAN BRACHIOPODA 69. Fig. 6. Diagrammatic views of (A) the ventral and (B) the dorsal interiors of Astraborthis. submedial lobes of diductor scars impressed on the floor of a strong pseudospondy- lium ; mantle canal pattern saccate. Dorsal interior with a simple plate-like cardinal process and short, blade-like outward-curving brachiophores embedded in a thick deposit of secondary shell; sockets oblique, notothyrial platform weak, fused with median ridge ; adductor scars quadripartite with smaller posterior pair ; man
. Bulletin of the British Museum (Natural History) Geology Supplement. ORDOVICIAN BRACHIOPODA 69. Fig. 6. Diagrammatic views of (A) the ventral and (B) the dorsal interiors of Astraborthis. submedial lobes of diductor scars impressed on the floor of a strong pseudospondy- lium ; mantle canal pattern saccate. Dorsal interior with a simple plate-like cardinal process and short, blade-like outward-curving brachiophores embedded in a thick deposit of secondary shell; sockets oblique, notothyrial platform weak, fused with median ridge ; adductor scars quadripartite with smaller posterior pair ; mantle canal pattern probably digitate. Type species. Astraborthis uniplicata sp. nov. from the Mytton Flags. Discussion. Although the new genus is obviously alimbellid in its general morphology, it differs from other members of the family in its ornament and certain aspects of its internal morphology. Externally it is immediately distinguishable from the smooth Alimbella and finely capillate Medesia in its coarse costellation and internally in the weak development of the notothyrial platform and the blade-like nature of the brachiophores. It further differs from Alimbella in its wide ventral adductor scar and from Medesia in the absence of branching and medial fusion of the proximal parts of the vascula media. It may be of familial significance that dental plates have not yet been seen in adult pedicle valves of any of the three genera assigned to the Alimbellidae. It is, however, possible that short receding dental plates were developed during early growth stages but were later entirely buried in thick deposits of secondary shell secreted in the delthyrial cavity during formation of the pseudospondylium. Until young shells or their impressions have been examined it is safer to delay assessing the importance of this aspect of alimbellid Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - colorat
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