﻿200 
  ACTINOPTttRYGII. 
  

  

  depth 
  of 
  the 
  trunk 
  nearly 
  equal 
  to 
  the 
  length 
  of 
  the 
  head 
  and 
  trunk 
  

   without 
  caudal 
  fin 
  ; 
  distance 
  from 
  frontal 
  angulation 
  to 
  hinder 
  margin 
  

   of 
  preoperculum 
  equalling 
  about 
  one-quarter 
  of 
  the 
  total 
  length 
  of 
  

   the 
  fish. 
  [Dentition 
  imperfectly 
  known, 
  but] 
  teeth 
  smooth, 
  some 
  

   indented, 
  and 
  those 
  of 
  the 
  principal 
  mandibular 
  series 
  at 
  least 
  twice 
  

   as 
  broad 
  as 
  long. 
  Dorsal 
  and 
  anal 
  fins 
  equally 
  elevated, 
  the 
  latter 
  

   with 
  about 
  30 
  rays 
  and 
  four-fifths 
  as 
  long 
  as 
  the 
  former, 
  which 
  has 
  35 
  

   rays. 
  Squamation 
  covering 
  less 
  than 
  half 
  of 
  the 
  trunk; 
  ridge-scales 
  

   coarsely 
  serrated, 
  each 
  on 
  the 
  ventral 
  aspect 
  with 
  about 
  six 
  points. 
  

  

  It 
  seems 
  probable 
  that 
  the 
  so-called 
  M 
  esc 
  don 
  gibbosus 
  1 
  is 
  founded 
  

   upon 
  a 
  small, 
  distorted 
  fish 
  of 
  this 
  species. 
  The 
  original 
  specimen 
  

   is 
  in 
  the 
  Palseontological 
  Museum, 
  Munich, 
  and 
  was 
  obtained 
  from 
  

   the 
  Lithographic 
  Stone 
  of 
  Kelheim. 
  Three 
  other 
  small 
  fishes 
  from 
  

   Eichstadt, 
  in 
  the 
  same 
  Museum, 
  also 
  probably 
  the 
  young 
  of 
  

   M. 
  macropterus, 
  bear 
  the 
  name 
  of 
  M. 
  pulcJiellus 
  (A. 
  Wagner, 
  loc. 
  cit. 
  

   vol. 
  ix. 
  1862, 
  p. 
  351). 
  Another 
  dwarf 
  variety, 
  from 
  the 
  Middle 
  

   Purbeck 
  of 
  Teffont, 
  Wiltshire, 
  is 
  named 
  M. 
  m,acropterus, 
  var. 
  parvus 
  

   (A. 
  S. 
  Woodward, 
  Geol. 
  Mag. 
  [4] 
  vol. 
  ii. 
  1895, 
  p. 
  147, 
  pi. 
  vii. 
  

   fig. 
  2). 
  

  

  Form. 
  Sf 
  Loc. 
  Lower 
  Kimmeridgian 
  (Lithographic 
  Stone) 
  : 
  

   Bavaria. 
  

  

  P. 
  5546. 
  Well-preserved 
  fish 
  0*14 
  in 
  length, 
  shown 
  of 
  two-thirds 
  the 
  

   natural 
  size 
  in 
  PI. 
  XVI. 
  fig. 
  1 
  ; 
  Eichstadt. 
  As 
  shown 
  in 
  

   side 
  view, 
  the 
  basi 
  cranial 
  axis 
  is 
  bent 
  sharply 
  downwards 
  

   at 
  the 
  front 
  of 
  the 
  orbit 
  (o.) 
  to 
  the 
  dentigerous 
  vomer 
  (v.) 
  ; 
  

   and 
  some 
  of 
  the 
  sutures 
  in 
  the 
  cranial 
  roof 
  can 
  be 
  dis- 
  

   tinguished. 
  The 
  limits 
  of 
  the 
  supraoccipital 
  (s.occ), 
  

   squamosal 
  (sq.)> 
  and 
  parietal 
  (pa.) 
  plates 
  are 
  quite 
  clear, 
  

   and 
  the 
  latter 
  element 
  bears 
  a 
  large 
  process 
  (x) 
  on 
  its 
  

   hinder 
  margin, 
  this 
  directed 
  backwards 
  and 
  subdivided 
  

   into 
  digitations 
  at 
  the 
  extremity. 
  The 
  operculum 
  (op.) 
  

   and 
  preoperculum 
  (p.op.) 
  are 
  imperfect, 
  but 
  their 
  relative 
  

   proportions 
  and 
  characteristic 
  radiating 
  markings 
  are 
  seen. 
  

   Some 
  of 
  the 
  long 
  hour-glass-shaped 
  basals 
  (b.) 
  in 
  the 
  

   pectoral 
  fin 
  can 
  also 
  be 
  observed. 
  There 
  are 
  no 
  scales 
  on 
  

   the 
  caudal 
  region, 
  and 
  the 
  endoskeleton 
  is 
  thus 
  well 
  

   exposed. 
  By 
  exchange, 
  1888. 
  

  

  1 
  A. 
  Wagner, 
  Abk. 
  k. 
  bay. 
  Akad. 
  Wiss., 
  math.-phys. 
  CI. 
  vol. 
  vi. 
  (1851), 
  

   pp. 
  52, 
  56, 
  pi. 
  iii. 
  fig. 
  2. 
  Gyrodus 
  gibbosus, 
  L. 
  Agassiz, 
  Poiss. 
  Foss. 
  vol. 
  ii. 
  pt. 
  ii. 
  

   1844, 
  p. 
  236 
  (name 
  only, 
  ex 
  Miinster, 
  MS.). 
  A 
  distorted 
  specimen 
  of 
  Mesodon 
  

   from 
  the 
  Lithographic 
  Stone 
  of 
  Cirin, 
  Am, 
  France, 
  is 
  also 
  described 
  under 
  the 
  

   same 
  specific 
  name 
  by 
  V. 
  Thiolliere, 
  Poiss. 
  Foss. 
  Bugey, 
  pt. 
  ii. 
  (1873), 
  p. 
  13, 
  

   pi. 
  ii. 
  fig. 
  12. 
  

  

  