﻿mackosemiid^e. 
  173 
  

  

  Ophiopsis 
  (according 
  to 
  the 
  description) 
  in 
  the 
  non-bifurcated 
  

   character 
  of 
  all 
  the 
  dorsal 
  fin-rays. 
  It 
  is 
  the 
  type 
  of 
  the 
  genus 
  and 
  

   species 
  Eusemius 
  beatce, 
  B. 
  Vetter, 
  Mittheil. 
  k. 
  mineral. 
  -geol. 
  Mus, 
  

   Dresden, 
  pt. 
  iv. 
  (1881), 
  p. 
  51, 
  pi. 
  i. 
  fig. 
  3. 
  The 
  length 
  of 
  the 
  head 
  

   with 
  opercular 
  apparatus 
  considerably 
  exceeds 
  the 
  maximum 
  depth 
  

   of 
  the 
  trunk 
  and 
  is 
  contained 
  little 
  more 
  than 
  three-and-a-half 
  

   times 
  in 
  the 
  total 
  length 
  of 
  the 
  fish. 
  The 
  dorsal 
  fin 
  comprises 
  about 
  

   32 
  rays; 
  and 
  11 
  free 
  supports 
  are 
  described 
  in 
  advance 
  of 
  this. 
  

   The 
  principal 
  flank-scales 
  are 
  delicately 
  sculptured, 
  exhibit 
  from 
  4 
  

   to 
  6 
  strong 
  denticulations 
  on 
  the 
  posterior 
  margin, 
  and 
  are 
  deeper 
  

   than 
  broad 
  ; 
  there 
  are 
  about 
  44 
  dorso-ventral 
  series. 
  

  

  The 
  published 
  notices 
  of 
  Ophiopsis 
  muensteri 
  (G. 
  von 
  Minister, 
  

   Neues 
  Jahrb. 
  1834, 
  p. 
  385 
  ; 
  L. 
  Agassiz, 
  Poiss. 
  Toss. 
  vol. 
  ii. 
  1844, 
  

   pt. 
  i. 
  p. 
  292, 
  pt. 
  ii. 
  p. 
  289 
  ; 
  A. 
  Wagner, 
  Abh. 
  k. 
  bay. 
  Akad. 
  Wiss., 
  

   math.-phys. 
  CI. 
  vol. 
  vi. 
  1851, 
  p. 
  60) 
  leave 
  the 
  systematic 
  position 
  of 
  

   this 
  species 
  doubtful. 
  According 
  to 
  Wagner's 
  description, 
  the 
  ver- 
  

   tebral 
  centra 
  are 
  well 
  ossified 
  ; 
  according 
  to 
  a 
  figure 
  by 
  von 
  Zittel, 
  

   who 
  names 
  the 
  species 
  Isopholis 
  muensteri 
  (Handb. 
  Palgeont. 
  vol. 
  iii. 
  

   1887, 
  p. 
  216, 
  fig. 
  230), 
  the 
  head 
  is 
  indistinguishable 
  from 
  that 
  of 
  

   Eugnaihus. 
  The 
  type 
  specimen, 
  obtained 
  from 
  the 
  Lithographic 
  

   Stone 
  of 
  Kelheim, 
  Bavaria, 
  is 
  an 
  elongated 
  fish 
  wanting 
  the 
  pelvic, 
  

   dorsal, 
  and 
  anal 
  fins 
  ; 
  it 
  is 
  preserved 
  in 
  the 
  Palaeontological 
  

   Museum, 
  Munich. 
  

  

  The 
  genus 
  Macrepistius 
  (E. 
  D. 
  Cope, 
  Journ. 
  Acad. 
  Nat. 
  Sci. 
  

   Philad. 
  [2] 
  vol. 
  ix. 
  1894, 
  p. 
  441), 
  so 
  far 
  as 
  known, 
  appears 
  to 
  differ 
  

   from 
  Ophiopsis 
  only 
  in 
  having 
  all 
  the 
  teeth 
  tumid 
  at 
  the 
  apex, 
  ex- 
  

   cept 
  those 
  of 
  the 
  premaxillae 
  and 
  the 
  opposing 
  portion 
  of 
  the 
  

   dentaries. 
  The 
  type 
  species 
  is 
  M. 
  arenatus 
  (E. 
  D. 
  Cope, 
  ibid. 
  

   p. 
  441, 
  pi. 
  xix. 
  fig. 
  2) 
  from 
  the 
  Neocomian 
  of 
  Glen 
  Eose, 
  Texas, 
  

   probably 
  attaining 
  a 
  length 
  of 
  about 
  0*3. 
  The 
  head 
  and 
  opercular 
  

   bones 
  are 
  ornamented 
  with 
  tubercles, 
  which 
  become 
  confluent 
  on 
  

   the 
  hinder 
  part 
  of 
  the 
  parietals. 
  The 
  operculum 
  is 
  twice 
  as 
  deep 
  

   as 
  broad 
  and 
  three 
  times 
  as 
  large 
  as 
  the 
  suboperculum. 
  The 
  

   dorsal 
  fin 
  originally 
  comprised 
  not 
  less 
  than 
  32 
  rays. 
  The 
  scales 
  

   are 
  irregularly 
  pitted, 
  but 
  not 
  serrated 
  on 
  the 
  hinder 
  margin. 
  

  

  Genus 
  HISTIONOTUS, 
  Egerton. 
  

   [Ann. 
  Mag. 
  Nat. 
  Hist. 
  [2] 
  vol. 
  xiii. 
  1854, 
  p. 
  434.] 
  

  

  Head 
  large, 
  snout 
  acute 
  ; 
  the 
  dorsal 
  margin 
  of 
  the 
  trunk 
  rising 
  

   above 
  the 
  head 
  to 
  an 
  angulation 
  from 
  which 
  the 
  body 
  gradually 
  

   tapers 
  backwards. 
  Marginal 
  teeth 
  much 
  elongated, 
  closely 
  ar- 
  

   ranged. 
  Notochord 
  invested 
  with 
  delicate 
  ring-vertebrae. 
  Fins 
  

  

  