. Bulletin of the British Museum (Natural History), Geology. 340 REVISION OF ACTINOPTERYGIAN AND COELACANTH FISHES exactly comparable to the theory put forward by Aldinger (1937 : 363), and Stensio bases it also on an interpretation of the three bones above the preopercular in Parasemionotus as being suborbitals derived from the anamestic components of the preopercular. His second theory is that the suborbitals of the Palaeoniscids and Subholostei have been directly inherited (Watson, 1925 : 868 ; 1928 : 58). For these suborbitals to acquire the Holostean condition, Stensio (from an interpreta
. Bulletin of the British Museum (Natural History), Geology. 340 REVISION OF ACTINOPTERYGIAN AND COELACANTH FISHES exactly comparable to the theory put forward by Aldinger (1937 : 363), and Stensio bases it also on an interpretation of the three bones above the preopercular in Parasemionotus as being suborbitals derived from the anamestic components of the preopercular. His second theory is that the suborbitals of the Palaeoniscids and Subholostei have been directly inherited (Watson, 1925 : 868 ; 1928 : 58). For these suborbitals to acquire the Holostean condition, Stensio (from an interpretation of Brough's, 1939 : 66, description of Ptycholepis curta ; Text-fig. 61) suggests that Ssc Exsc Pa Scl Op CI. Smx Pope Fig. 63. Promecosomina formosa (Woodward). Skull in lateral view, after Wade (1941). they underwent an excessive outgrowth backwards, over the anterior portion of the preopercular, which was consequently reduced. Then as the anterior portion of the preopercular was eliminated, the superficial sensory lines (supramaxillary and postmaxillary) carried thereon would have been forced to shift to the skin laterally to the suborbitals, and would thus become secondarily situated outside these bones. Schaeffer & Dunkle (1950 : 21) summing up the evidence, believe that the palaeontological data alone would favour Stensio's second theory for the origin of Holostean suborbitals. In 1952 Lehman described three new Parasemionotid genera from the basal. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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