PLATE LIV. 



Fig. Page. 



1. Ptychodus aff. mortoni, Mantell; imperfect crown of tooth, oral and 



(la) anterior views, nat. size. — Chalk; Winchester. Oxford 

 Museum. 244. 



2. Pachyrhizodus sp. ; lower portion of head and opercular apparatus, left- 



side view, nat. size. — Zone of Holaster subr/lobosus ; South Ferriby, 

 Lincolnshire. Collection of Henry C. Drake, Esq., F.G.S. br., 

 branchiostegal rays; d., dentary; lop., interoperculum; irue.., maxilla; 

 pmx., premaxilla; po., postorbital plate; }><>}>., preoperculum ; qu., 

 quadrate ; sop., suboperculum. 249. 



3. Dentition probably of parasphenoid of an Elopine or Albulid fish, oral 



view, nat. size, with (3 a) three teeth enlarged three times. — Zone 

 of Holaster subglobosus ; Wouldham, Kent. G. E. Dibley Collec- 

 tion (B. M. no. P. 10952). 250. 



4. Apateodus striatum, A. S. Woodward; head, left side view, with (4<?) 



upper view of skull, three quarters nat. size. — Zone of Holaster sub- 

 globosus ; Brockham, Surrey. Museum of Practical Geology, ao., 

 antorbital ; epo., epiotic ; etli., mesethmoid ; Jr., frontal; top., inter- 

 operculum ; pa., parietal; pi., palatine; po., postorbital; scl., 

 sclerotic ; so., suborbital ; socc, supraoccipital ; sop., suboperculum. 24(>. 



5. Gyrodus (?) cretaceus, Agassiz ; mandible with dentition, oral view, nat. 



size, with inner (5 a) and outer (5 b) views of the coronoid end of 

 the right splenial, also nat. size, and a posterior principal tooth (5 c) 

 and an anterior tooth (5t7) in side view, twice nat. size. — Zone of 

 Terebratulina gracilis ; Cuxton, Kent. Collection of George 

 Hutchings, Esq. 251. 



