LEPID0GAN01DEI. 155 



into and beyond its middle part, supporting a kind of slender 

 appendage between the two normal lobes. Coelacanths are 

 most abundant in the Devonian and carboniferous forma- 

 tions ; but some occur in oolitic and even in cretaceous beds ; 

 but all became extinct before the tertiary epoch. 



Fine specimens of homocercal fishes, with rounded ganoid 

 scales, sculptured externally and pierced by pro- 

 minent mucus-tubes, as in fig. 65, have been 

 discovered in the chalk formations of Kent and 

 Sussex. They have been referred by Agassiz to 

 the genus called Macropoma, significative of the lg ' 



° Macropoma 



large size of the gill-cover, and to the ccelacanthal Mantelli 

 family. Casts of the " interior" of the alimentary ^ ia '" 

 canal, shewing impressions of a broad spiral valve, are pre- 

 served in certain specimens in the British Museum. One 

 species (M. Egertoni) is from the Speeton clay; the other 

 (M. Mantelli) from the chalk. 



Codacanthus is represented by species in carboniferous 

 (C. Upturns), permian (C. granulosus), and 

 triassic (C. minor) beds. 



Glyptolepis had a heterocercal tail, with 

 rounded scales, smooth externally, and with 

 radiating compartments internally. The G. mi- 

 crolepidotus, of which a magnified view of some 

 scales is given in fig. 66, occurs in the middle 

 old red sandstone of Scotland and Eussia. 



Phyllolepis is, as yet, known only by its Fl s- 66 - 



-, ,-, , • -,-, r. j -, Glyptolepis micro- 



large smooth or concentrically furrowed scales, upidotus (De- 

 some of which are six inches in diameter. voman )- 

 Ph. concentricus occurs in the upper old red of Clashbinnie ; 

 Aster olepis in the middle old red of Elgin ; Bothriolepis in 

 the upper old red of Scotland and Eussia ; and Glyptopomus, 

 with the cranial bones sculptured externally, in the upper old 

 red of Dura Den. 



