. The Cambridge natural history. Zoology. XVIII CHONDROSTEI 487 of the lower jaw are dentigerous. Except for the absence of an interoperculum, the opercular series of bones is complete, includ- ing numerous branchiostegal rays. There is a single small median jugular plate. The Palaeoniscidae are remarkable both for their individual and specific abundance and for their extensive range in time. Eepresented only by Cheirolepis in the Middle Old Eed Sandstone and Devonian, the family attained its maximum development in the later Palaeozoic rocks (Carboniferous and Lower Permian), became rare in th
. The Cambridge natural history. Zoology. XVIII CHONDROSTEI 487 of the lower jaw are dentigerous. Except for the absence of an interoperculum, the opercular series of bones is complete, includ- ing numerous branchiostegal rays. There is a single small median jugular plate. The Palaeoniscidae are remarkable both for their individual and specific abundance and for their extensive range in time. Eepresented only by Cheirolepis in the Middle Old Eed Sandstone and Devonian, the family attained its maximum development in the later Palaeozoic rocks (Carboniferous and Lower Permian), became rare in the Mesozoic, finally dwindling away at the close of the Jurassic period. Their geographical distribution in the past is hardly less remarkable. In various geological formations they have been found in Great Britain and Ireland, in widely remote parts of continental Europe, and in North America, South Africa, and Australia. Cheirolepis, Ambly- pterus, CanoMus, Fhanerosteon, JElonichthys, Crypliiolepis, Palaeo- niscus, and Trissolepis are Palaeozoic genera. Gyrolepis, Urolepis, Coccolepis, Oxygnatlius, and Centrolepis are characteristic Meso- zoic forms. Fam. 2. Platysomidae.^—More or less deep-bodied Fishes, with elongated dorsal and anal fins, a high head, short Fig. 285.—Restoration of Eurynotus crenatus. , Infra-clavicle ; , lateral line ; orh, orbit; otter reference letters as in Fig. 284. (From Traquair.) usually armed with bluntly conical tritoral teeth, and a complete investment of high, narrow, rhombic scales. They agree with the Palaeoniscidae in their osteology and in most other essential 1 Traquair, Trans. Roy. Soc. Edini. xxix. 1879, p. 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 Harmer, S. F. (Sidney Frederic), Sir, 1862- ed; Shipley, A. E. (Arthur Everett), Sir, 1861-
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