﻿ADDENDA 
  ET 
  CORRIGENDA. 
  533 
  

  

  doubt 
  from 
  the 
  specimens 
  recorded 
  below 
  that 
  the 
  fish 
  truly 
  

   belongs 
  to 
  this 
  Chondrostean 
  family 
  ; 
  a 
  catalogue 
  of 
  the 
  specimens 
  

   in 
  the 
  Collection 
  is 
  therefore 
  appended 
  here. 
  The 
  upper 
  lobe 
  of 
  

   the 
  tail, 
  the 
  fin-supports, 
  and 
  the 
  axial 
  skeleton 
  of 
  the 
  trunk 
  still 
  

   remain 
  unknown 
  ; 
  but 
  the 
  demonstrated 
  arrangement 
  of 
  the 
  cheek- 
  

   plates 
  appears 
  to 
  suffice 
  for 
  determining 
  the 
  systematic 
  position 
  of 
  

   the 
  genus. 
  

  

  Genus 
  PLATYSIAGUM, 
  Egerton. 
  

  

  [Pigs. 
  & 
  Descript. 
  Brit. 
  Organic 
  Remains, 
  dec. 
  xiii. 
  (Mem. 
  

  

  Geol, 
  Surv. 
  1872), 
  no. 
  6.] 
  

  

  Trunk 
  elongate-fusiform. 
  Mandibular 
  suspensorium 
  oblique 
  ; 
  

   dentition 
  consisting 
  of 
  a 
  series 
  of 
  large, 
  well-spaced 
  conical 
  teeth, 
  

   and 
  numerous 
  smaller 
  teeth 
  irregularly 
  arranged 
  and 
  somewhat 
  

   clustered 
  ; 
  head 
  and 
  opercular 
  bones 
  externally 
  tuberculated, 
  

   clavicular 
  bones 
  partly 
  rugose. 
  Fins 
  of 
  moderate 
  size, 
  with 
  

   numerous 
  small 
  fulcra, 
  the 
  rays 
  broad, 
  all 
  much 
  bifurcated 
  and 
  

   closely 
  articulated 
  distally. 
  Pelvic 
  tins 
  short-based 
  ; 
  dorsal 
  fin 
  

   about 
  as 
  long 
  as 
  deep, 
  arising 
  opposite 
  or 
  nearly 
  opposite 
  the 
  pelvic 
  

   pair 
  ; 
  [anal 
  fin 
  unknown] 
  • 
  caudal 
  fin 
  deeply 
  forked. 
  Scales 
  thin, 
  

   small 
  or 
  of 
  moderate 
  size, 
  and 
  several 
  ventral 
  series 
  very 
  narrow 
  ; 
  

   ornament 
  comprising 
  feeble, 
  slightly-radiating 
  ridges 
  towards 
  the 
  

   hinder 
  margin, 
  and 
  sparsely 
  scattered 
  tubercles 
  on 
  the 
  anterior 
  

   portion. 
  

  

  Platysiagum 
  sclerocephalum, 
  Egerton. 
  

  

  18?2. 
  Platysiagum 
  sclerocephalum, 
  Sir 
  P. 
  Egerton, 
  loc. 
  cit. 
  no. 
  6, 
  pi. 
  vi. 
  

  

  Type. 
  Imperfect 
  distorted 
  fish 
  ; 
  British 
  Museum. 
  

  

  The 
  tyj>e 
  species 
  attaining 
  a 
  length 
  of 
  about 
  06. 
  Form 
  and 
  

   proportions 
  unknown, 
  but 
  head 
  with 
  opercular 
  apparatus 
  large 
  and 
  

   its 
  length 
  much 
  exceeding 
  the 
  maximum 
  depth 
  of 
  the 
  trunk. 
  

   Tubercular 
  ornament 
  almost 
  disappearing 
  on 
  the 
  hinder 
  portion 
  of 
  

   the 
  operculum 
  and 
  suboperculum 
  and 
  on 
  the 
  branchiostegal 
  rays, 
  

   coarsest 
  and 
  partly 
  replaced 
  by 
  rugae 
  on 
  the 
  clavicular 
  arch 
  ; 
  very 
  

   fine 
  tubercles 
  also 
  on 
  the 
  two 
  foremost 
  rays 
  of 
  the 
  pectoral 
  fin. 
  

   Maximum 
  depth 
  of 
  hinder 
  expansion 
  of 
  maxilla 
  equalling 
  about 
  

   one-third 
  of 
  the 
  total 
  length 
  of 
  the 
  bone, 
  and 
  the 
  dentigerous 
  border 
  

   slightly 
  sinuous 
  ; 
  teeth 
  smooth 
  ; 
  suboperculum 
  much 
  more 
  than 
  half 
  

   as 
  deep 
  as 
  the 
  operculum. 
  Pectoral 
  fin 
  with 
  about 
  20, 
  and 
  pelvic 
  

   fin 
  with 
  about 
  10 
  rays, 
  the 
  latter 
  half 
  as 
  deep 
  as 
  the 
  former 
  ; 
  dorsal 
  

   fin 
  with 
  at 
  least 
  16 
  rays, 
  arising 
  opposite 
  a 
  point 
  immediately 
  be- 
  

   hind 
  the 
  pelvic 
  pair. 
  Tuberculations 
  on 
  scales 
  very 
  sparse. 
  

  

  Form. 
  <Sf 
  Loc. 
  Lower 
  Lias 
  :. 
  Dorsetshire. 
  

  

  