ORDERS CHIMEROIDEI AND DIPNOI. 



951 



median one ; while there is a spine on the rostrum. Edaphodon, 

 which ranges from the Lower Greensand to the Middle Eocene of 

 Bracklesham, like the last genus, attains gigantic dimensions, but 

 has its teeth adapted entirely for crushing. The .mandibular tooth 

 (fig. 878) is very massive, and has its symphysial surface (which in 

 the preceding genera is narrow and grooved) very wide and quite 

 flat, while there are two outer and one median tritors, as well as a 

 terminal tritor which is not shown in the figure. Each palatal tooth 

 is furnished with three tritors. Teeth of this genus are common in 

 several Cretaceous and Tertiary deposits. E/asmodus, which is 

 found in the Lower and Middle Eocene of England, appears to be 



Fig. 



[nner surface of the right mandibular tooth ot Edaphodon gigas ; from the English 

 Chalk. Reduced. (After Egerton.) 



allied to the preceding genus ; while in the existing Callorhynchus 

 we apparently have the most specialised representative of the group 

 with crushing teeth. The latter genus is represented by an existing 

 species in the Southern seas, and by a fossil one from the Lower 

 Cretaceous of New Zealand. The mandibular tooth is massive, 

 with a narrow symphysis, and only a single tritor, representing the 

 large median one of Edaphodon. Other European forms are Gan- 

 odus, from the Lower Jurassic of Stonesfield, in which the tritors of 

 the mandibular tooth are confluent ; and Myriacanthtts (Prognath- 

 odus or Metopacanthus), of the Lower Lias of Dorsetshire, which is 

 known both by the spines and the teeth. Its premaxillary teeth are 

 chisel-like in shape. Leptacanthus of the Lias, and Dipristis of the 

 Middle Miocene, are imperfectly known forms probably referable to 

 this family. In North America the names Ewnylodus, Leptomylus, 

 Byactinus, Diphrissa, Isotcenia, and Sphageoposa have been applied 

 to Cretaceous forms, while a Miocene type has been called Mylo- 

 gnathus ; but there is considerable doubt whether all these forms are 

 really distinct from European genera. 



As genera of which the family position is uncertain may be men- 

 tioned Chimceropsis from the Lower Kimeridgian of Bavaria, which 

 differs from existing forms by its shagreen skin, and apparently also 



VOL. II. E 



