. Bulletin of the British Museum (Natural History), Geology. 362 REVISION OF ACTINOPTERYGIAN AND COELACANTH FISHES Fifthly, Elonichthys shows a limited development of ridge scales similar to that condition found in Acentrofihorus, and lastly, Elonichthys still has its full complement of branchiostegal rays, and they are not reduced as in Mesopoma. From the above facts it is clear that although Elonichthys is a long way off that grade of organization seen in Acentrophorus, it does show changes of the right nature. It is quite unlikely that the family Elonichthyidae is ancestral to the Semionoto
. Bulletin of the British Museum (Natural History), Geology. 362 REVISION OF ACTINOPTERYGIAN AND COELACANTH FISHES Fifthly, Elonichthys shows a limited development of ridge scales similar to that condition found in Acentrofihorus, and lastly, Elonichthys still has its full complement of branchiostegal rays, and they are not reduced as in Mesopoma. From the above facts it is clear that although Elonichthys is a long way off that grade of organization seen in Acentrophorus, it does show changes of the right nature. It is quite unlikely that the family Elonichthyidae is ancestral to the Semionotoidea but until new forms are found (from the Lower Permian) which establish clearer relationships, then as far as can be seen they are about the only family from which the Semionotoidea could be derived. ASPIDORHYNCHOIDEA The fourth group of Holosteans to be dealt with, the Aspidorhynchoidea, includes the single family Aspidorhynchidae. This family ranges from the Middle Jurassic to the Upper Cretaceous. In it are included two closely-allied genera, Aspidorhynchus and Belonostomus (Text-fig. 76). Both these genera are highly specialized on their Ssc, Pa Spt I Dsp + lnf \ / ,Fr c ..So. S°P / -Inf Br ,op Pop Smx Fig. 76. Belonostomus tenuirostris Agassiz. Restoration of skull in lateral view, after Saint-Seine (1949). first appearance, possessing elongated bodies and snouts, and deepened flank scales. In Aspidorhynchus the rostrum is produced well beyond the mandibular symphysis, but in Belonostomus (Saint-Seine, 1949, fig. 114) the rostrum is only just longer than the mandible. The skull roof in both genera is typically Holostean and there is a dermosphenotic in Belonostomus tenuirostris, although Rayner (1941 : 229) indicates that it is missing or fused with the frontals in some species of Aspidorhynchus. In contrast the extrascapular is seemingly absent in Belonostomus. There is only one series of bones (three in number) between the eye and the preopercular in Belonostomus, a
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