﻿BELONOEHYN-CHID^. 
  15 
  

  

  powerful; 
  superficial 
  ornament 
  consisting 
  of 
  short 
  rugae, 
  the 
  

   majority 
  directed 
  longitudinally. 
  Operculum 
  two-thirds 
  as 
  broad 
  

   as 
  deep. 
  Scutes 
  of 
  dorsal 
  and 
  ventral 
  series 
  long, 
  narrow, 
  and 
  

   slender, 
  apparently 
  smooth. 
  

  

  Form. 
  6f 
  Loc. 
  Upper 
  Lias 
  : 
  Yorkshire. 
  Lower 
  Lias 
  : 
  Dorsetshire. 
  

  

  Except 
  the 
  first, 
  all 
  the 
  following 
  specimens 
  were 
  obtained 
  from 
  

   Lower 
  Lias 
  of 
  the 
  neighbourhood 
  of 
  Lyme 
  "Regis. 
  

  

  P. 
  4268. 
  Type 
  specimen, 
  being 
  the 
  fragmentary 
  cranium 
  figured 
  by 
  

   Agassiz, 
  loc. 
  cit. 
  fig. 
  4 
  ; 
  Upper 
  Lias, 
  Whitby. 
  

  

  Enniskillen 
  Coll. 
  

  

  P. 
  428. 
  Crushed 
  and 
  somewhat 
  fractured 
  head, 
  lateral 
  aspect, 
  

   measuring 
  0145 
  in 
  length, 
  but 
  wanting 
  the 
  extremity 
  of 
  

   the 
  snout. 
  The 
  laniary 
  teeth 
  gradually 
  become 
  more 
  and 
  

   more 
  robust 
  backwards, 
  and 
  those 
  of 
  the 
  two 
  jaws 
  alternate, 
  

   fitting 
  into 
  broad 
  notches 
  ; 
  the 
  clusters 
  of 
  minute 
  inter- 
  

   vening 
  denticles 
  are 
  conspicuous. 
  The 
  imperfectly 
  pre- 
  

   served 
  angular 
  bone 
  of 
  the 
  mandible 
  is 
  shown 
  to 
  be 
  

   continuous 
  with 
  the 
  articular 
  element. 
  Purchased, 
  1882. 
  

  

  43054. 
  Smaller 
  head, 
  0*1 
  in 
  length, 
  the 
  cranium 
  much 
  crushed 
  but 
  

   showing 
  the 
  extension 
  of 
  the 
  roof-bones 
  beyond 
  the 
  

   occiput 
  posteriorly. 
  The 
  jaws 
  are 
  almost 
  of 
  equal 
  length, 
  

   the 
  mandible 
  being 
  not 
  more 
  than 
  0*002 
  shorter 
  than 
  the 
  

   upper 
  jaw. 
  The 
  angular 
  bone 
  displays 
  its 
  truncated 
  but 
  

   gently 
  rounded 
  postero-inferior 
  border, 
  and 
  also 
  exhibits 
  

   the 
  series 
  of 
  vertically-extended 
  markings 
  due 
  to 
  the 
  per- 
  

   forations 
  of 
  a 
  sensory 
  canal. 
  Purchased, 
  1871. 
  

  

  P. 
  3791. 
  A 
  fine 
  example 
  of 
  the 
  head, 
  with 
  left 
  operculum 
  and 
  

   clavicle, 
  shown 
  of 
  the 
  natural 
  size 
  in 
  PI. 
  II. 
  fig. 
  1. 
  Be- 
  

   sides 
  displaying 
  the 
  general 
  proportions, 
  this 
  specimen 
  

   also 
  exhibits 
  a 
  few 
  details, 
  notably 
  the 
  post-occipital 
  

   extension 
  of 
  the 
  cranial 
  roof 
  (r.), 
  the 
  presence 
  of 
  cheek- 
  

   plates, 
  the 
  position 
  of 
  the 
  narial 
  opening 
  (n.), 
  and 
  the 
  

   form 
  of 
  the 
  articulo-angular 
  bone. 
  The 
  operculum 
  (op.) 
  is 
  

   nearly 
  one 
  and 
  a 
  half 
  times 
  as 
  deep 
  as 
  broad, 
  tapering 
  

   downwards, 
  and 
  evidently 
  not 
  succeeded 
  either 
  by 
  a 
  sub- 
  

   operculum 
  or 
  branchiostegal 
  rays. 
  The 
  clavicle 
  (cl.) 
  is 
  

   deep, 
  narrow 
  and 
  gently 
  arched, 
  with 
  a 
  relatively 
  large 
  

   but 
  narrow 
  triangular 
  plate 
  extending 
  far 
  backwards 
  from 
  

   the 
  hinder 
  border. 
  Enniskillen 
  Coll. 
  

  

  P. 
  985. 
  Somewhat 
  smaller 
  head, 
  lateral 
  aspect, 
  with 
  operculum 
  and 
  

   clavicle. 
  Egerton 
  Coll. 
  

  

  