﻿418 
  Wieland 
  — 
  Evolution 
  of 
  the 
  Testudinate 
  Humerus. 
  

  

  between 
  such 
  forms 
  as 
  Lytoloma 
  and 
  Toxochelys 
  on 
  the 
  marine 
  

   side, 
  and 
  the 
  humerus 
  of 
  Chelydra, 
  a 
  chelie 
  or 
  land 
  form 
  modi- 
  

   fied 
  as 
  has 
  been 
  previously 
  noted, 
  in 
  the 
  direction 
  of 
  natatorial 
  

   types. 
  It 
  is 
  of 
  course 
  possible 
  that 
  the 
  flippered 
  Gryptodira 
  

   represent 
  several 
  lines 
  of 
  descent 
  from 
  land 
  forms, 
  each 
  having 
  

   distinct, 
  but 
  in 
  the 
  main, 
  parallel 
  characters. 
  

  

  Another 
  very 
  distinct 
  thalassoid 
  form 
  which 
  may 
  well 
  be 
  

   mentioned 
  here 
  is 
  the 
  "turtle-like 
  humerus" 
  from 
  the 
  Cre- 
  

   taceous 
  near 
  Columbus, 
  Mississippi, 
  figured 
  by 
  Leidy 
  and 
  at 
  

   first 
  referred 
  by 
  him 
  to 
  the 
  Mosasauria 
  (12).* 
  As 
  will 
  be 
  

   seen 
  on 
  comparing 
  figs. 
  6, 
  9, 
  and 
  10, 
  this 
  fossil 
  presents 
  

   decided 
  approximations 
  to 
  Lytoloma, 
  there 
  being 
  however 
  dis- 
  

   tally 
  more 
  suggestion 
  of 
  distinctly 
  oceanic 
  types. 
  

  

  The 
  humerus 
  of 
  Toxochelys 
  latiremis 
  figured 
  by 
  Case 
  (4) 
  is 
  

   a 
  suggestive 
  thalassoid 
  form 
  characteristic 
  of 
  the 
  older 
  Che- 
  

   loniidw 
  and 
  closely 
  nearing 
  typical 
  oceanic 
  outlines. 
  

  

  With 
  regard 
  to 
  these 
  two 
  transitional 
  forms, 
  the 
  chelicoid 
  

   and 
  thalassoid, 
  it 
  may 
  be 
  said 
  that 
  they 
  fairly 
  bridge 
  over 
  the 
  

   fundamental 
  differences 
  between 
  the 
  humeri 
  of 
  the 
  existing 
  

   marine 
  and 
  land 
  Testudinata. 
  The 
  number 
  of 
  complete 
  skele- 
  

   tons 
  is 
  as 
  yet 
  so 
  meager 
  that 
  the 
  facts 
  can 
  only 
  be 
  presented 
  in 
  

   a 
  general 
  way. 
  

  

  Turtle 
  humeri 
  of 
  intermediate 
  type 
  are 
  common 
  in 
  the 
  Cre- 
  

   taceous 
  of 
  New 
  Jersey, 
  but 
  there 
  is 
  a 
  dearth 
  of 
  knowledge 
  con- 
  

   cerning 
  the 
  forms 
  to 
  which 
  they 
  belong, 
  the 
  collections 
  

   consisting 
  as 
  yet 
  mainly 
  in 
  hopeless 
  fragments 
  gathered 
  from 
  

   the 
  surface 
  by 
  untrained 
  collectors, 
  whose 
  efforts 
  usually 
  result 
  

   in 
  the 
  destruction 
  of 
  the 
  clues 
  to 
  completer 
  specimens. 
  

  

  Ihe 
  Typical 
  Oceanic, 
  or 
  Thalassic 
  and 
  Parathalassic 
  Humeri. 
  

  

  The 
  thalassic, 
  or 
  form 
  of 
  humerus 
  seen 
  in 
  the 
  living 
  Ohe- 
  

   loniidce, 
  is 
  a 
  widely 
  distributed 
  one 
  and 
  may 
  be 
  considered 
  as 
  

   the 
  true 
  or 
  generalized 
  ocean 
  type. 
  Yariations 
  of 
  this 
  form 
  

   are 
  seen 
  in 
  the 
  Protostegidce 
  of 
  Cope 
  (6), 
  and 
  the 
  Desmato- 
  

   chelyidce 
  of 
  Williston 
  (19, 
  20). 
  Cf. 
  figs. 
  13, 
  17, 
  19, 
  and 
  22 
  in 
  

   the 
  present 
  text. 
  

  

  * 
  Leidy 
  has 
  explained 
  in 
  an 
  interesting 
  manner 
  how 
  at 
  a 
  time 
  when 
  the 
  limbs 
  

   of 
  the 
  Mosasaurs 
  were 
  yet 
  unknown, 
  both 
  Cope 
  and 
  himself, 
  as 
  well 
  as 
  Agassiz, 
  

   had 
  mistakenly 
  concurred 
  in 
  a 
  belief 
  in 
  the 
  Mosasauran 
  character 
  of 
  this 
  fossil 
  

   (13). 
  Cope 
  was, 
  however, 
  the 
  first 
  to 
  refer 
  to 
  its 
  Testudinate 
  nature 
  under 
  the 
  

   name 
  Protostega 
  tuberosa 
  (6). 
  While 
  the 
  type 
  specimen 
  has 
  not 
  been 
  seen 
  by 
  the 
  

   writer, 
  there 
  is 
  no 
  suggestion 
  that 
  this 
  humerus 
  is 
  not 
  Testudinate 
  and 
  natatorial 
  

   in 
  character. 
  Baur 
  has 
  said 
  that 
  it 
  cannot 
  belong 
  to 
  the 
  Cheloniidce 
  (2). 
  Neither 
  

   can 
  it 
  belong 
  to 
  Cope's 
  Protostegidce, 
  nor 
  to 
  Agassiz's 
  genus 
  Attantochelys 
  as 
  finally 
  

   proposed 
  by 
  Leidy 
  (13). 
  Cf. 
  figs. 
  14-16 
  and 
  9 
  and 
  10 
  in 
  text. 
  This 
  humerus 
  

   lacks 
  at 
  the 
  present 
  time 
  a 
  generic 
  name. 
  Necessarily 
  retaining 
  Cope's 
  species, 
  I 
  

   shall 
  call 
  the 
  turtle 
  to 
  which 
  it 
  belongs 
  Neptunochelys 
  tuberosa. 
  

  

  