PLATE XVIII. 



Fig. Page. 



1. Ctenothrissa radians (Agassiz) ; imperfect fisli deepened by distortion, 



exhibiting the vertebral column. — English Chalk. B. M. no. P. 390. 

 c, caudal fin; ch, clavicle; d., dentary ; do., remains of dorsal fin; 

 nix., maxilla; smx. 1, 2., anterior and posterior supramaxilla. 81. 



2. Ditto; portion of hyoid arch, right lateral aspect. — Probably from a 



Turonian zone; Sussex. Dixon Collection (B. M. no. 25936). br., 

 upper branchiostegal rays; ch., ceratohyal (only hinder end correct 

 shape) ; eph., epihyal. 80. 



3. Ditto; ceratohyal (ch.) with branchiostegal raj^s (br.). — Zone of Holaster 



subglobosus; Clayton Tunnel, Sussex. Bright Collection (B. M. no. 

 44836 a). 80. 



4. Ditto; urohyal, left lateral aspect. — Zone of Holaster subglobosus; 



Burham, Kent. B. M. no. 47911. 80. 



5. Ditto; one of the foremost flank-scales and some further back (5a), 



twice nat. size. — Probably from a Turonian zone; near Lewes. 

 Mantell Collection (type specimen, B. M. no. 4029). 82. 



6. Ctenothrissa microcephala (Agassiz) ; left lateral aspect of fish, with dis- 



torted head and only bases of fins. English Chalk. B. M. no. P. 392. 

 a., anal fin ; c, caudal fin; do., dorsal fin; op., operculum; ph., pelvic 

 fins. 84. 



7. Ditto ; ventral aspect of fish, showing pelvic fins (ph.). — Zone of Holaster 



subglobosus; Burham. Toulmin Smith Collection (B. M. no. 41689). 84. 



8. Ditto ; flank-scale, twice nat. size. — Zone of Holaster subglobosus ; 



Reigate, Surrey. Capron Collection (B. M. no. 49881). 85. 



9. Ditto ; flank- scales, three times nat. size. — Probably from a Turonian 



zone; Sussex. Dixon Collection (B. M. no. 25887). 84. 



All the figures, except 5, ha, 8, 9, of the natural size. 



