﻿42 
  

  

  ACTINOPTEKYGII. 
  

  

  P. 
  2262 
  e, 
  P. 
  3358. 
  Polished 
  sections 
  of 
  similar 
  rays 
  ; 
  from 
  Sands- 
  

   end, 
  near 
  Whitby. 
  Egerton 
  Sf 
  Enniskillen 
  Colls. 
  

  

  P. 
  3356 
  n. 
  Series 
  of 
  unjointed 
  rays, 
  the 
  longest 
  piece 
  preserved 
  0*5 
  

   in 
  length, 
  probably 
  forming 
  the 
  anterior 
  part 
  of 
  the 
  

   pectoral 
  fin. 
  The 
  foremost 
  rays 
  gradually 
  increase 
  in 
  

   length, 
  terminating 
  successively 
  on 
  the 
  anterior 
  border 
  ; 
  

   and 
  the 
  two 
  parallel 
  rods 
  of 
  which 
  each 
  is 
  composed 
  are 
  

   fused 
  together 
  at 
  the 
  pointed 
  distal 
  end. 
  

  

  Ennishillen 
  Coll. 
  

  

  Several 
  more 
  imperfect 
  bones 
  of 
  Gyrosteus 
  mirabilis 
  from 
  the 
  

   Enniskillen 
  Collection 
  are 
  also 
  registered 
  under 
  the 
  general 
  number 
  

   P. 
  3356. 
  

  

  All 
  the 
  typical 
  examples 
  of 
  Gyrosteus 
  are 
  contained 
  in 
  an 
  

   indurated 
  matrix 
  * 
  ; 
  but 
  evidence 
  of 
  a 
  smaller 
  Chondrostean, 
  very 
  

   probably 
  of 
  the 
  same 
  genus, 
  is 
  also 
  found 
  in 
  a 
  soft 
  shale 
  in 
  the 
  

   Whitby 
  cliffs. 
  The 
  following 
  are 
  a 
  few 
  specimens 
  : 
  — 
  

  

  P. 
  3357. 
  Hyomandibular 
  0*18 
  in 
  length. 
  Ennishillen 
  Coll. 
  

  

  P. 
  3356 
  0. 
  Crushed 
  right 
  clavicle, 
  inner 
  aspect, 
  about 
  0*1 
  in 
  depth. 
  

  

  Enniskillen 
  Coll. 
  

  

  P. 
  2262 
  d. 
  Left 
  supraclavicle, 
  inner 
  aspect, 
  nearly 
  0*3 
  in 
  maximum 
  

   depth, 
  differing 
  from 
  that 
  of 
  G. 
  mirabilis 
  in 
  being 
  com- 
  

   paratively 
  narrow. 
  Egerton 
  Coll. 
  

  

  P. 
  3356 
  p. 
  Undetermined 
  bone. 
  Enniskillen 
  Coll. 
  

  

  Family 
  ACIPENSEBIDiE. 
  

  

  Trunk 
  elongate 
  or 
  elongate-fusiform 
  ; 
  tail 
  heterocercal. 
  External 
  

   head-bones 
  well 
  developed, 
  those 
  of 
  the 
  cranial 
  roof 
  forming 
  a 
  con- 
  

   tinuous 
  shield, 
  which 
  comprises 
  a 
  median 
  longitudinal 
  series 
  of 
  

   azygous 
  elements 
  ; 
  snout 
  prominent 
  and 
  eye 
  far 
  forwards 
  • 
  mouth 
  

   small, 
  inferior, 
  and 
  suctorial, 
  without 
  teeth 
  in 
  the 
  adult 
  ; 
  no 
  pre- 
  

   maxilla 
  ; 
  operculum 
  present, 
  but 
  no 
  branchiostegal 
  rays. 
  Squamation 
  

   of 
  trunk 
  comprising 
  few 
  longitudinal 
  series 
  of 
  overlapping 
  bony 
  

   scutes, 
  with 
  irregular 
  intermediate 
  small 
  stellate 
  ossifications 
  ; 
  the 
  

   lateral 
  rhombic 
  scales 
  and 
  large 
  fulcral 
  scales 
  on 
  the 
  upper 
  caudal 
  

   lobe 
  robust. 
  

  

  * 
  This 
  was 
  probably 
  obtained 
  from 
  the 
  bed 
  immediately 
  above 
  the 
  Jet 
  

   Bock 
  (M. 
  Simpson, 
  Foss. 
  Yorkshire 
  Lias, 
  ed. 
  2, 
  1884, 
  p. 
  adii). 
  

  

  