PLATE XXTI. 



Pig, Page. 



1. Plethodus expansus, Dixon; lower dental plate, oral face, two thirds 



nat. size, and view of tnbercnlated rim (1 a), nat. size. — Cambridge 

 Greensand. B. M. no. 35309. 108. 



2. Ditto ; upper dental plate, oral face, aboral face (2 a), and posterior end 



view (2 b), two thirds nat. size. — Chalk ; Kent. B. M. no. 38585. 



]>., ascending median bony process; x., lateral bony plate. 108. 



3. Ditto; upper dental plate, aboral face, two thirds nat. size. — Probably 



zone of Holaster subglobosus ; near Maidstone. Bowerbank Collec- 

 tion (B. M. no. 30091). p., ascending median bony process. 108. 

 1-. Ditto ; portion of vertical section of upper dental plate, showing tubules 

 and surface-layer. — Zone of Holaster subglobosus ; Hailing, Kent. 

 B. M. no. 43079. 108. 



5. Ditto ; transverse section of three dentinal tubules, highly magnified. — 



Chalk; South Wiltshire. Cunnington Collection (B. M. no. 40392). 108. 



6. Plethodus pentagon, A. S. Woodward; lower dental plate, oral face, with 



portion of vertical section, nat. size (G a), and with portion of 

 abraded oral face showing tubules, magnified twenty times (0 h). 

 Type specimen. — Zone of Holaster subglobosus ; Burham, Kent. 

 Toulmin Smith Collection (B. M. no. 41716 a). 109. 



7. Ditto ; pointed end of lower dental plate, oral face, showing pittings. — 



Ibid. B. M. no. 47947. 109. 



8. Ditto ; upper dental plate, oral face, with view of pitted and tuberculated 



lateral face (8a). — Chalk; Kent. Harford Collection (B. M. no. 

 P. 5G26). 109. 



( .». Plethodus oblongus, Dixon; imperfect head, right and left (9 a) lateral 

 aspects. — Zone of Holaster subglobosus; Clayton, Sussex. Willett 

 Collection no. 154, Brighton Museum. <!., dentary ; fr., frontal ; 

 hm., hyomandibular ; /., portion of lower dental plate; m., mucus-pit; 

 op., operculum ; os., orbitosphenoid ; pa., parietal ; pas., parasphenoid; 

 pop., preoperculum ; sq., squamosal; v., upper dental plate; x., supra- 

 occipital (?). 110. 

 1 0. Ditto ; imperfect head, left lateral aspect, with end of rostrum in front 

 view (10a). — Zone of Holaster subglobosus; Dorking, Surrey. 

 Capron Collection (B. M. no. 49895). co., two upper plates of 

 circumorbital ring; eept., ectopterygoid ; eth., mesethmoid ; mx., 

 maxilla; s.t., supratemporals ; uli., urohyal ; other letters as in fig. 9. 110. 



Unless otherwise stated, the figures are of the natural size. 



