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  ItlR. 
  E. 
  LYDEKKER 
  ON 
  REMAINS 
  OF 
  EOCENE 
  AND 
  MESOZOIC 
  

  

  that 
  the 
  shell 
  alone 
  is 
  insufficient 
  to 
  afford 
  certain 
  generic 
  characters. 
  

   For 
  the 
  same 
  reason 
  the 
  term 
  Propleura 
  of 
  Cope 
  (1870) 
  must 
  be 
  re- 
  

   jected. 
  We 
  have, 
  however, 
  the 
  name 
  Lytoloma, 
  Cope, 
  based 
  on 
  the 
  

   evidence 
  of 
  the 
  mandible, 
  and 
  which 
  is 
  earlier 
  than 
  Glossoohdys, 
  

   Seeley 
  (1871), 
  which 
  was 
  based 
  on 
  the 
  skull. 
  There 
  is, 
  indeed, 
  the 
  

   name 
  Puppigerus, 
  Cope 
  (1870). 
  The 
  type 
  of 
  that 
  genus 
  must 
  be 
  

   taken 
  to 
  be 
  Chelone 
  longiceps, 
  Owen, 
  as 
  being 
  the 
  first-mentioned 
  of 
  

  

  Fig. 
  2. 
  — 
  Ventral 
  and 
  Lateral 
  Aspects 
  of 
  the 
  Imperfect 
  Mandible 
  of 
  

   Lytoloma 
  cantabrigiense 
  ; 
  from 
  the 
  Cambridge 
  Greensand. 
  

   (Nat. 
  size.) 
  

  

  the 
  English 
  Eocene 
  forms 
  on 
  which 
  that 
  genus 
  is 
  based. 
  Now 
  the 
  

   skull 
  of 
  that 
  form, 
  as 
  I 
  have 
  recently 
  found, 
  is 
  similar 
  to 
  that 
  of 
  the 
  

   young 
  of 
  the 
  so-called 
  Chelone 
  crassicostata, 
  one 
  of 
  the 
  typical 
  forms 
  

   of 
  Euclastes 
  ; 
  and 
  Puppigerus 
  is 
  therefore 
  a 
  synonym 
  of 
  the 
  latter. 
  

   The 
  names 
  Lytoloma 
  and 
  Puppigerus 
  occur 
  in 
  the 
  same 
  volume 
  ; 
  but 
  

   since 
  the 
  former 
  comes 
  first, 
  and 
  the 
  latter 
  includes 
  forms 
  which 
  

   are 
  distinct, 
  I 
  propose 
  to 
  adopt 
  Lytoloma 
  in 
  the 
  place 
  of 
  Euclastes. 
  

  

  I 
  may 
  also 
  mention 
  that 
  in 
  young 
  individuals, 
  and 
  perhaps 
  in 
  the 
  

   adult 
  of 
  some 
  of 
  the 
  apparently 
  smaller 
  forms, 
  like 
  L. 
  trigoniceps 
  of 
  

   the 
  Bracklesham 
  beds, 
  the 
  mandibular 
  symphysis 
  (as 
  shown 
  by 
  a 
  

   specimen 
  in 
  the 
  Museum 
  of 
  Practical 
  Geology) 
  is 
  shorter 
  and 
  more 
  

   convex 
  than 
  in 
  the 
  adult 
  of 
  L. 
  crassicostatum 
  and 
  L. 
  planimentum, 
  and 
  

   is 
  thus 
  almost 
  similar 
  to 
  the 
  mandible 
  of 
  Thalassochelys. 
  

  

  In 
  these 
  respects 
  the 
  present 
  mandible 
  agrees 
  very 
  closely 
  with 
  

  

  