﻿PYCNODONTIDJS. 
  223 
  

  

  teeth. 
  Vertebral 
  axis 
  at 
  origin 
  of 
  dorsal 
  fin 
  midway 
  between 
  the 
  

   dorsal 
  and 
  ventral 
  borders 
  of 
  the 
  fish. 
  Dorsal 
  fin 
  with 
  more 
  than 
  

   50 
  rays, 
  occupying 
  considerably 
  more 
  than 
  half 
  of 
  the 
  back, 
  much 
  

   more 
  elevated 
  than 
  the 
  anal 
  fin, 
  which 
  has 
  45 
  rays, 
  and 
  the 
  length 
  

   of 
  which 
  equals 
  about 
  three-quarters 
  that 
  of 
  the 
  dorsal. 
  Ridge- 
  

   scales 
  coarsely 
  serrated 
  ; 
  flank-scales 
  delicate, 
  marked 
  with 
  feeble 
  

   rugae, 
  which 
  are 
  mostly 
  transverse. 
  

  

  A 
  small 
  fish 
  in 
  the 
  Palaeontological 
  Museum, 
  Munich, 
  not 
  

   improbably 
  young 
  of 
  this 
  species, 
  is 
  named 
  Microdon 
  nanus, 
  A. 
  

   Wagner, 
  he. 
  cit. 
  vol. 
  ix. 
  (1862) 
  p, 
  344. 
  

  

  Form, 
  fy 
  Log. 
  Lower 
  Kimmeridgian 
  (Lithographic 
  Stone) 
  : 
  Bavaria. 
  

  

  37369. 
  Plaster 
  cast 
  of 
  type 
  specimen 
  ; 
  Kelheim. 
  Purchased, 
  1863. 
  

  

  P. 
  1628, 
  P. 
  3764. 
  Pine 
  large 
  specimen 
  partly 
  in 
  counterpart, 
  

   showing 
  remains 
  of 
  the 
  pelvic 
  fins 
  ; 
  Solenhofen. 
  

  

  Egerton 
  and 
  EnnisHllen 
  Colls. 
  

  

  P. 
  1631. 
  Caudal 
  region, 
  with 
  nearly 
  complete 
  caudal 
  fin 
  ; 
  Kelheim. 
  

  

  Egerton 
  Coll. 
  

  

  P. 
  3765. 
  Imperfect 
  caudal 
  fin 
  ; 
  Kelheim. 
  EnnisHllen 
  Coll. 
  

  

  Microdon 
  radiatus, 
  Agassiz. 
  

  

  1839-44. 
  Microdon 
  radiatus, 
  L. 
  Agassiz, 
  Poiss. 
  Foss. 
  vol. 
  ii. 
  pt. 
  ii. 
  

  

  p. 
  208, 
  pi. 
  lxix. 
  c. 
  figs. 
  1, 
  2. 
  

   1840. 
  Microdon 
  radiatus, 
  R. 
  Owen, 
  Odontography, 
  p. 
  73, 
  pi. 
  xliii. 
  fig. 
  1. 
  

  

  Type. 
  Imperfect 
  fishes. 
  

  

  A 
  much 
  smaller 
  species 
  than 
  the 
  type, 
  nearly 
  similar 
  in 
  general 
  

   form 
  and 
  proportions, 
  but 
  with 
  relatively 
  deeper 
  abdominal 
  region. 
  

   Principal 
  series 
  of 
  splenial 
  teeth 
  wider 
  than 
  the 
  two 
  outer 
  series, 
  

   of 
  which 
  the 
  outermost 
  is 
  considerably 
  the 
  largest. 
  Ridge-scales 
  

   with 
  three 
  or 
  four 
  coarse 
  serrations, 
  of 
  which 
  the 
  hindermost 
  

   is 
  a 
  large 
  denticle; 
  flank-scales 
  robust, 
  marked 
  with 
  prominent 
  

   rugae 
  which 
  are 
  mostly 
  transverse 
  and 
  radiating. 
  

  

  The 
  laminar 
  expansions 
  on 
  the 
  neural 
  and 
  haemal 
  arches 
  are 
  

   well 
  shown 
  in 
  several 
  specimens 
  recorded 
  below, 
  proving 
  that 
  their 
  

   absence 
  in 
  the 
  original 
  fossils 
  examined 
  by 
  Agassiz 
  was 
  accidental. 
  

   The 
  neural 
  spines 
  are 
  remarkably 
  robust 
  in 
  the 
  abdominal 
  region. 
  

  

  Form. 
  Sf 
  Log. 
  Purbeckian 
  : 
  Dorsetshire. 
  

  

  All 
  the 
  following 
  specimens 
  were 
  obtained 
  from 
  the 
  neighbour- 
  

   hood 
  of 
  Swanage 
  : 
  — 
  

  

  19013. 
  Pish 
  0*105 
  in 
  length, 
  wanting 
  the 
  pelvic 
  fins 
  and 
  the 
  

   greater 
  part 
  of 
  the 
  dorsal 
  and 
  anal 
  fins. 
  Purchased, 
  1844. 
  

  

  