﻿1064 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  8hell-substance 
  impunctate 
  externally, 
  but 
  the 
  inner 
  laminae 
  

   are 
  sparsely 
  perforated. 
  

  

  Type, 
  Stringocephalus 
  Burtini, 
  Def 
  ranee. 
  Middle 
  Devonian 
  

  

  Tropidoleptus, 
  Hall. 
  1857. 
  

   (Plate 
  54, 
  figs. 
  1-11.) 
  

  

  Shells 
  with 
  the 
  general 
  external 
  aspect 
  of 
  Kafinesquina 
  ; 
  con- 
  

   cavo-, 
  or 
  plano-convex. 
  Hinge-line 
  straight; 
  in 
  young 
  shells 
  

   forming 
  the 
  greatest 
  transverse 
  diameter 
  and 
  frequently 
  extended 
  

   at 
  the 
  cardinal 
  extremities, 
  but 
  in 
  mature 
  and 
  old 
  shells 
  shorter 
  

   than 
  the 
  transverse 
  diameter 
  in 
  the 
  pallial 
  region. 
  Marginal 
  

   outline 
  varying 
  from 
  longitudinally 
  semi-elliptical 
  in 
  youth, 
  to 
  

   transversely 
  subelliptical 
  at 
  maturity. 
  Surface 
  covered 
  with 
  

   simple, 
  low 
  plications, 
  all 
  extending 
  from 
  beak 
  to 
  margins. 
  The 
  

   median 
  plication 
  on 
  the 
  pedicle-valve 
  and 
  the 
  corresponding 
  

   sinus 
  on 
  the 
  brachial 
  valve 
  are 
  broader 
  and 
  more 
  conspicuous 
  

   than 
  the 
  others. 
  

  

  The 
  pedicle- 
  valve 
  is 
  regularly 
  convex, 
  becoming 
  slightly 
  con- 
  

   cave 
  on 
  the 
  cardinal 
  slopes. 
  It 
  bears 
  a 
  moderately 
  broad 
  cardi- 
  

   nal 
  area, 
  coextensive 
  with 
  the 
  hinge-line, 
  which 
  is 
  divided 
  by 
  a 
  

   broad, 
  open 
  delthyrium, 
  which, 
  in 
  no 
  observed 
  condition 
  of 
  

   growth, 
  bears 
  a 
  covering 
  of 
  any 
  sort, 
  but 
  is 
  filled 
  by 
  the 
  cardinal 
  

   process 
  of 
  the 
  other 
  valve. 
  The 
  base 
  of 
  the 
  delthyrial 
  cavity 
  is 
  

   thickened 
  and 
  transversely 
  striated, 
  probably 
  by 
  the 
  attachment 
  

   of 
  the 
  pedicle-muscle. 
  The 
  teeth 
  are 
  not 
  situated 
  at 
  the 
  extremi- 
  

   ties 
  of 
  the 
  delthyrial 
  margins, 
  but 
  lie 
  within 
  and 
  in 
  front 
  of 
  them, 
  

   arise 
  from 
  the 
  bottom 
  of 
  the 
  valve 
  as 
  two 
  erect, 
  divergent 
  sub- 
  

   quadrate 
  crests, 
  resting 
  upon 
  low 
  ridges 
  which 
  bound 
  the 
  muscu- 
  

   lar 
  area. 
  These 
  peculiar 
  teeth 
  are 
  smooth 
  and 
  abrupt 
  on 
  their 
  

   inner 
  faces, 
  while 
  their 
  outer 
  faces 
  are 
  deeply 
  crenulated. 
  A 
  

   low 
  groove 
  separates 
  each 
  from 
  the 
  cardinal 
  area. 
  The 
  muscular 
  

   area 
  is 
  broadly 
  flabellate, 
  extending 
  more 
  than 
  half 
  way 
  across 
  

   the 
  valve, 
  and 
  consists 
  of 
  two 
  large 
  diductor 
  scars 
  enclosing 
  a 
  

   narrow 
  median 
  pair 
  of 
  adductors. 
  

  

  The 
  brachial 
  valve 
  is 
  slightly 
  concave, 
  often 
  nearly 
  flat. 
  Cardi- 
  

   nal 
  area 
  narrow, 
  but 
  clearly 
  developed; 
  chilidium 
  prominent. 
  

   Cardinal 
  process 
  large, 
  erect, 
  smooth 
  on 
  its 
  posterior 
  surface, 
  and 
  

  

  122 
  

  

  