﻿220 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Genus 
  aechmina 
  Jones 
  & 
  Holl 
  

  

  [Ety.: 
  ac/fj.rj, 
  point 
  of 
  a 
  spear] 
  

  

  (An. 
  and 
  mag. 
  nat. 
  hist. 
  ser. 
  4. 
  3:217) 
  

  

  Carapace 
  with 
  thick 
  valves, 
  straight 
  at 
  hinge 
  hne, 
  rounded 
  at 
  the 
  

   ends, 
  and 
  convex 
  at 
  the 
  ventral 
  border. 
  Surface 
  drawn 
  out 
  into 
  a 
  

   broad-based 
  and 
  sharp 
  pointed 
  hollow 
  cone, 
  which 
  either 
  involves 
  

   the 
  whole 
  surface, 
  or 
  rises 
  from 
  the 
  postero-dorsal 
  or 
  centro-dorsal 
  

   region. 
  

  

  Aechmina 
  spinosa 
  (Hall) 
  (Fig. 
  152). 
  Cytherinaspinosa 
  

   Hall 
  (1852. 
  Pal. 
  N. 
  Y. 
  2:317, 
  pi. 
  67) 
  

  

  Distinguishing 
  characters. 
  Strong 
  oblique 
  spine, 
  

   thick 
  and 
  hollow 
  at 
  the 
  base, 
  either 
  elongate 
  or 
  

   short; 
  pointed 
  upward, 
  outward 
  and 
  forward, 
  and 
  

   sometimes 
  slightly 
  bent; 
  valves 
  thickened 
  on 
  the 
  

   free 
  border 
  by 
  a 
  raised, 
  rounded 
  but 
  irregular 
  mar- 
  

   gin; 
  area 
  at 
  base 
  of 
  spine 
  hollow 
  and 
  smooth; 
  

   raised 
  margin 
  sometimes 
  punctate; 
  spine 
  often 
  long 
  

   and 
  projecting 
  beyond 
  the 
  upper 
  margin 
  of 
  the 
  

   valve. 
  

  

  Found 
  in 
  weathered 
  Rochester 
  shale 
  on 
  the 
  talus 
  

   Pig. 
  152 
  Aechmina 
  ^^ 
  ^^^ 
  Romc, 
  Watertowu 
  and 
  Ogdensburg 
  railroad 
  

   *^After^ones^"^^^^^ 
  cut 
  abovc 
  Lcwistou. 
  The 
  valves 
  are 
  often 
  im- 
  

   bedded 
  in 
  the 
  shale 
  with 
  the 
  inner 
  concave 
  surfaces 
  exposed. 
  Also 
  

   found 
  at 
  Lockport 
  (Hall). 
  

  

  Order 
  TRILOBITA 
  Burmeister 
  

  

  The 
  trilobites 
  are 
  extinct 
  Crustacea, 
  wholly 
  confined 
  to 
  the 
  Paleo- 
  

   zoic 
  seas. 
  The 
  body 
  was 
  covered 
  with 
  a 
  carapace 
  longitudinally 
  

   divisible 
  into 
  three 
  parts. 
  The 
  anterior 
  portion 
  comprises 
  the 
  head- 
  

   shield, 
  or 
  cephalon, 
  which 
  is 
  usually 
  semicircular, 
  with 
  a 
  straight 
  pos- 
  

   terior 
  border. 
  The 
  central 
  of 
  the 
  three 
  cephalic 
  lobes 
  is 
  the 
  glabella, 
  

   which 
  is 
  the 
  most 
  prominent 
  part 
  of 
  the 
  cephalon. 
  It 
  is 
  of 
  varying 
  

   outline, 
  and 
  more 
  or 
  less 
  divided 
  by 
  transverse 
  furrows 
  or 
  pairs 
  of 
  

   furrows. 
  The 
  last 
  furrow 
  is 
  the 
  occipital 
  furrozv, 
  and 
  delimits 
  the 
  

   occipital 
  rm^, 
  which 
  is 
  just 
  anterior 
  to 
  the 
  first 
  segment 
  cf 
  the 
  thorax. 
  

   On 
  either 
  side 
  of 
  the 
  glabella 
  is 
  a 
  pair 
  of 
  cheeks, 
  divided 
  by 
  the 
  

   facial 
  suture 
  into 
  fixed 
  cheeks 
  (those 
  next 
  to 
  the 
  glabella) 
  and 
  free 
  

   cheeks 
  (the 
  outermost 
  portion). 
  The 
  latter 
  are 
  often 
  prolonged 
  into 
  

  

  