﻿FROM 
  THE 
  RED 
  CRAG 
  OF 
  SUFFOLK. 
  3 
  

  

  deep 
  median 
  hollow; 
  but 
  the 
  crista 
  galli 
  and 
  the 
  cribriform 
  plates 
  

   are 
  broken 
  away, 
  giving 
  full 
  view 
  into 
  the 
  nasal 
  cavities, 
  divided 
  as 
  

   usual 
  posteriorly 
  by 
  a 
  horizontal 
  partition 
  (P.) 
  into 
  an 
  upper 
  or 
  

   " 
  olfactory 
  chamber 
  " 
  and 
  a 
  lower 
  or 
  " 
  narial 
  passage." 
  The 
  lateral 
  

   portions 
  of 
  this 
  partition 
  formed 
  by 
  the 
  palate-bones 
  (PL.) 
  still 
  remain, 
  

   but 
  its 
  central 
  part, 
  together 
  with 
  the 
  whole 
  of 
  the 
  vomer, 
  has 
  dis- 
  

   appeared. 
  In 
  the 
  middle 
  of 
  the 
  roof 
  of 
  the 
  olfactory 
  chamber 
  the 
  

   upper 
  part 
  of 
  the 
  stout 
  septum 
  formed 
  by 
  the 
  strongly 
  ossified 
  

   mesethmoid 
  (ME.) 
  remains 
  ; 
  and 
  a 
  prominent 
  longitudinal 
  ridge 
  

   (ET.) 
  on 
  the 
  lateral 
  wall, 
  but 
  preserved 
  on 
  the 
  right 
  side, 
  is 
  all 
  that 
  

   indicates 
  the 
  turbinals. 
  The 
  whole 
  of 
  the 
  sphenoids 
  and 
  their 
  

   dependencies 
  and 
  the 
  pterygoids 
  are 
  broken 
  away, 
  the 
  fracture 
  ex- 
  

   tending 
  through 
  the 
  bodies 
  of 
  the 
  palate-bones, 
  just 
  behind 
  the 
  pos- 
  

   terior 
  molar 
  teeth. 
  

  

  The 
  upper 
  surface 
  (fig. 
  2) 
  includes 
  the 
  whole 
  extent 
  of 
  the 
  frontals, 
  

   except 
  the 
  aritero-lateral 
  processes 
  which 
  form 
  the 
  upper 
  margin 
  of 
  

   the 
  orbit, 
  which 
  have 
  been 
  worn 
  away. 
  It 
  is 
  probably 
  also 
  due 
  to 
  

   attrition 
  that 
  the 
  general 
  surface 
  is 
  evenly 
  convex 
  from 
  side 
  to 
  side, 
  

   instead 
  of 
  laterally 
  ridged 
  and 
  flat 
  or 
  even 
  concave 
  in 
  the 
  centre 
  as 
  

   in 
  the 
  existing 
  species. 
  The 
  anterior 
  edge 
  of 
  this 
  surface, 
  forming 
  

   the 
  upper 
  boundary 
  of 
  the 
  anterior 
  nares, 
  is 
  evenly 
  arched, 
  showing 
  

   no 
  median 
  process 
  as 
  in 
  the 
  Manati, 
  and 
  to 
  a 
  less 
  extent 
  in 
  the 
  

   Dugong 
  ; 
  but 
  this 
  may 
  also 
  be 
  due 
  to 
  the 
  wearing 
  off 
  of 
  the 
  thin 
  part 
  

   of 
  the 
  edges 
  of 
  the 
  bones. 
  A 
  nearly 
  semicircular 
  suture 
  an 
  inch 
  

   behind 
  this 
  margin 
  appears 
  plainly 
  to 
  mark 
  off 
  a 
  distinct 
  pair 
  of 
  

   nasal 
  bones 
  (Net.), 
  joining 
  each 
  other 
  in 
  the 
  middle 
  line 
  and 
  therefore 
  

   widely 
  differing 
  from 
  their 
  rudimentary 
  or 
  suppressed 
  condition 
  in 
  

   recent 
  Sirenians. 
  But, 
  as 
  is 
  well 
  known, 
  in 
  some 
  species 
  of 
  Hali- 
  

   iherium 
  they 
  are 
  developed 
  as 
  conspicuously 
  as 
  in 
  the 
  present 
  

   example*. 
  The 
  size 
  and 
  form 
  of 
  the 
  anterior 
  nasal 
  aperture 
  (fig. 
  3) 
  

   is 
  characteristically 
  Sirenian, 
  and 
  in 
  its 
  height 
  compared 
  with 
  its 
  

   breadth 
  more 
  like 
  that 
  of 
  Memettus 
  than 
  Hetlicore. 
  Its 
  boundary 
  on 
  

   the 
  right 
  side 
  by 
  the 
  ascending 
  process 
  of 
  the 
  prsemaxilla 
  (PMx.) 
  is 
  

   well 
  seen 
  ; 
  but 
  on 
  the 
  left 
  this 
  is 
  broken 
  away 
  ; 
  and, 
  as 
  before 
  men- 
  

   tioned, 
  the 
  anterior 
  boundary 
  with 
  the 
  greater 
  part 
  of 
  the 
  rostrum 
  

   has 
  unfortunately 
  perished. 
  The 
  floor 
  of 
  the 
  cavity 
  has 
  precisely 
  

   the 
  same 
  general 
  form 
  as 
  in 
  the 
  recent 
  Sirenians. 
  

  

  The 
  lateral 
  surface 
  of 
  the 
  fragment 
  (fig. 
  4) 
  shows 
  the 
  inner 
  wall 
  

   of 
  the 
  anterior 
  part 
  of 
  the 
  temporal 
  fossa, 
  and 
  of 
  the 
  orbit, 
  the 
  

   prominent 
  margins 
  of 
  the 
  last-named 
  cavity 
  and 
  the 
  zygoma 
  being 
  

   removed, 
  and 
  the 
  great 
  anteorbital 
  foramen 
  thus 
  converted 
  into 
  an 
  

   open 
  groove. 
  This 
  region 
  presents 
  a 
  striking 
  difference 
  of 
  conform- 
  

   ation 
  from 
  both 
  of 
  the 
  existing 
  genera. 
  In 
  Hcdicore, 
  in 
  the 
  dried 
  

   skull, 
  there 
  is 
  a 
  very 
  large 
  vacuity 
  between 
  the 
  frontal 
  and 
  maxillary 
  

   bones, 
  connecting 
  the 
  orbital 
  cavity 
  with 
  the 
  nasal 
  fossa. 
  In 
  the 
  

   genus 
  Memettus 
  this 
  vacuity 
  is 
  greatly 
  reduced, 
  the 
  thin 
  edges 
  of 
  the 
  

   two 
  bones, 
  in 
  the 
  form 
  of 
  delicate 
  paper-like 
  laminse, 
  uniting 
  more 
  

   or 
  less 
  completely 
  in 
  different 
  skulls. 
  In 
  the 
  present 
  fossil 
  specimen 
  

  

  * 
  H. 
  Schinzi, 
  Kaup, 
  ' 
  Beitrage 
  zur 
  naheren 
  Kenntniss 
  der 
  urweltlichen 
  Sau- 
  

   gethiere,' 
  Heft 
  ii. 
  1855, 
  tab. 
  ii. 
  fig. 
  2. 
  

  

  b2 
  

  

  