﻿48 
  ACTXNOPTERTGII. 
  

  

  Munich, 
  the 
  writer 
  is 
  now 
  inclined 
  to 
  withdraw 
  his 
  comparison 
  of 
  

   this 
  fossil 
  with 
  the 
  supposed 
  rostrum 
  of 
  those 
  fishes 
  (see 
  supra, 
  

   Pt. 
  II. 
  p. 
  395). 
  

  

  Form. 
  Sf 
  Log. 
  Senonian 
  : 
  Kent. 
  

  

  33221-24. 
  Type 
  specimen, 
  being 
  a 
  portion 
  of 
  the 
  tail 
  described 
  and 
  

   figured, 
  loc. 
  tit. 
  ; 
  Upper 
  Chalk, 
  Gravesend. 
  The 
  largest 
  

   caudal 
  fulcral 
  scale 
  measures 
  0-024 
  in 
  maximum 
  breadth, 
  

   and 
  0"027 
  from 
  the 
  apex 
  to 
  the 
  bifurcation 
  of 
  the 
  base. 
  

  

  Taylor 
  Coll. 
  

  

  Division 
  B. 
  — 
  Baseosts 
  rudimentary 
  or 
  absent 
  in 
  pelvic 
  fins 
  ; 
  

   dermal 
  rays 
  of 
  dorsal 
  and 
  anal 
  fins 
  equal 
  in 
  number 
  to 
  

   the 
  endoskeletal 
  supporting 
  elements 
  ; 
  tail 
  never 
  hetero- 
  

   cercal, 
  usually 
  abbreviate-heterocercal 
  or 
  homocercal, 
  

   rarely 
  diphycercal. 
  

  

  Suborder 
  II. 
  PROTOSPONDYLL 
  

  

  Notochord 
  persistent, 
  or 
  if 
  more 
  or 
  less 
  replaced 
  by 
  vertebrae, 
  

   the 
  pleurocentra 
  and 
  hypocentra 
  in 
  part 
  of 
  the 
  caudal 
  region 
  re- 
  

   maining 
  distinct 
  and 
  alternating 
  even 
  when 
  fully 
  developed 
  ; 
  tail 
  

   abbreviate-heterocercal. 
  Mandible 
  complex, 
  with 
  well-developed 
  

   splenial 
  rising 
  into 
  a 
  coronoid 
  process, 
  which 
  is 
  completed 
  by 
  a 
  

   distinct 
  coronoid 
  bone. 
  Infraclavicular 
  plates 
  wanting 
  in 
  the 
  

   pectoral 
  arch 
  ; 
  pectoral 
  fin 
  with 
  more 
  than 
  five 
  basals. 
  Scales 
  

   ganoid. 
  In 
  the 
  living 
  forms 
  — 
  air-bladder 
  connected 
  with 
  the 
  

   oesophagus 
  in 
  the 
  adult, 
  optic 
  nerves 
  not 
  decussating, 
  but 
  forming 
  a 
  

   chiasma, 
  and 
  intestine 
  with 
  a 
  spiral 
  valve. 
  

  

  Synopsis 
  of 
  Families. 
  

  

  I. 
  Mandibular 
  suspensoriurn 
  vertical 
  or 
  in- 
  

   clined 
  forwards 
  and 
  gape 
  of 
  mouth 
  

   small. 
  

   Trunk 
  more 
  or 
  less 
  deeply 
  fusiform; 
  

   vertebrae 
  not 
  more 
  than 
  rings 
  ; 
  teeth 
  

   styliform 
  or 
  tritoral; 
  fulcra 
  large, 
  

   and 
  dorsal 
  fin 
  not 
  extending 
  more 
  

  

  than 
  half 
  the 
  length 
  of 
  the 
  trunk 
  . 
  . 
  Semionotidje 
  (p. 
  49). 
  

   Trunk 
  elongate 
  or 
  elongate-fusiform 
  ; 
  

   vertebras 
  not 
  more 
  than 
  rings 
  ; 
  teeth 
  

   styliform 
  ; 
  fulcra 
  variable, 
  and 
  dorsal 
  

   fin 
  extending 
  at 
  least 
  half 
  the 
  length 
  

   of 
  the 
  trunk 
  Macrosemiid^ 
  (p. 
  163). 
  

  

  