138 



ORDERS OF FISHES. 



j)lates. The Pycnodonts {Pycnodus, Gyrodus, Ccelodus, Meso- 

 don, &c.) are principally Jurassic ; but there are various 

 Cretaceous forms, and a few Eocene and ]\Iiocene types are 



Fig. 504.— Under surface of the vomer of Ccelodus gyrodoides, .sliowing the rows of 

 cru.shiiig teeth. Cretaceous. (After Sir Philip Egerton.) 



known. The Triassic Flacodus, formerly referred to this 

 family, is now known to be truly Eeptilian. 



Sub-order C. Platysomid.e.i — The fishes included in 

 this division are mainly Carboniferous and Permian, and 

 have a close general resemblance to the Pycnodonts. The 

 body is deep and compressed ; and the scales are rhom- 



^ The separation of the Pycnodonts and PJatysomidce, and tlie elevation of 

 the latter to the rank of a distinct division of Ganoids are in accordance with 

 the views of Dr Traquair, our greatest authority upon the subject of the fossil 

 fishes. In this connection the author has to return his best thanks to Dr 

 Traquair for the permission to make tise of his researches on this subject, 

 which will shortly appear in the ' Transactions of the Royal Society of Edin- 

 burgh,' but which are as yet unpublislied. The author has also to gratefully 

 acknowledge much other friendly assistance as regards the fossil fishes from 

 the same sotirce. 



