﻿Report 
  of 
  the 
  State 
  Geologist. 
  1121 
  

  

  beds, 
  are 
  double-spiraled 
  athyroids; 
  Kayseria, 
  of 
  the 
  middle 
  

   Devonian, 
  which 
  is 
  the 
  only 
  double-spiraled 
  form 
  known 
  in 
  the 
  

   Palaeozoic, 
  appears 
  to 
  be 
  an 
  aberrant 
  and 
  accelerated 
  representa- 
  

   tive 
  of 
  the 
  stock 
  which 
  by 
  more 
  gradual 
  development 
  produced 
  

   Ketzia 
  and 
  Eiaietria. 
  

  

  Only 
  one 
  large 
  group 
  of 
  spire-bearing 
  shells 
  retains 
  the 
  cardinal 
  

   area, 
  namely, 
  the 
  Spiriferidje:. 
  a 
  family 
  with 
  everted 
  spirals, 
  one 
  

   of 
  the 
  earliest 
  to 
  appear 
  and 
  the 
  last 
  to 
  disappear. 
  Its 
  abundant 
  

   representatives 
  possess 
  the 
  longest 
  of 
  spirals 
  and 
  for 
  the 
  most 
  

   part 
  these 
  are 
  greatly 
  extended 
  transversely, 
  held 
  at 
  arm's 
  length, 
  

   as 
  it 
  were, 
  unsupported 
  by 
  a 
  connecting 
  jugum 
  (except 
  in 
  the 
  

   more 
  sparsely 
  represented 
  genera 
  Cyrtixa 
  and 
  Spiriferixa), 
  but 
  

   in 
  spite 
  of 
  the 
  delicacy 
  of 
  the 
  structure, 
  its 
  apparent 
  mechanical 
  

   disadvantages 
  in 
  the 
  absence 
  of 
  a 
  continuous 
  jugum, 
  this 
  type 
  of 
  

   structure 
  has 
  maintained 
  its 
  distinctive 
  character 
  and 
  multiplied 
  

   in 
  a 
  most 
  remarkable 
  manner. 
  

  

  The 
  relations 
  of 
  the 
  brachiopods 
  with 
  spiral 
  brachidia, 
  to 
  

   the 
  Axcylobrachia, 
  or 
  those 
  shells 
  commonly 
  spoken 
  of 
  as 
  the 
  

   terebratuloids, 
  has 
  been 
  a 
  fruitful 
  subject 
  of 
  discussion 
  and 
  

   given 
  rise 
  to 
  investigations 
  of 
  great 
  astuteness 
  and 
  merit. 
  

   Reference 
  has 
  already 
  been 
  made 
  to 
  the 
  facts 
  established 
  by 
  

   Beecher 
  and 
  Schuchekt 
  from 
  the 
  development 
  of 
  the 
  brachidium 
  

   in 
  Zygospira, 
  which 
  shorr 
  that 
  this 
  atrypid 
  passes 
  through 
  

   a 
  growth- 
  stage 
  in 
  which 
  the 
  brachidium 
  has 
  a 
  simple 
  terebratuloid 
  

   form, 
  similar 
  to 
  that 
  in 
  the 
  mature 
  condition 
  of 
  Dielasxla 
  ; 
  that 
  

   the 
  spirals 
  are 
  formed 
  by 
  the 
  continued 
  growth 
  of 
  the 
  descending 
  

   lamellse 
  of 
  the 
  loop 
  beyond 
  the 
  point 
  of 
  their 
  recurvature 
  into 
  

   the 
  ascending 
  lamellae. 
  What 
  is 
  thus 
  true 
  of 
  Zyoospira 
  we 
  must 
  

   assume 
  to 
  have 
  been 
  true 
  of 
  the 
  Helicopeomata 
  generally, 
  and 
  

   the 
  analogies 
  thus 
  established 
  between 
  them 
  and 
  the 
  loop-bearing 
  

   shells 
  are 
  these; 
  — 
  the 
  entire 
  loop 
  in 
  Dielasma, 
  Cryptoxella, 
  etc., 
  

   corresponds 
  to 
  that 
  portion 
  of 
  the 
  brachidium, 
  in 
  the 
  spire-bear- 
  

   ing 
  forms, 
  which 
  lies 
  behind 
  the 
  anterior 
  basal 
  edges 
  of 
  the 
  jugum; 
  

   the 
  descending 
  lamella? 
  of 
  the 
  former 
  represent 
  only 
  the 
  posterior 
  

   portion 
  of 
  the 
  primary 
  lamella? 
  of 
  the 
  latter, 
  while 
  the 
  ascending 
  

   lamella? 
  and 
  transverse 
  connecting 
  band 
  of 
  the 
  Axcylobrachia 
  

   are 
  the 
  equivalent 
  of 
  the 
  jugum 
  in 
  the 
  spire- 
  bearers. 
  The 
  spirals, 
  

   however, 
  are 
  a 
  later 
  development 
  in 
  the 
  individual, 
  and 
  are 
  hence 
  

   undoubtedly 
  a 
  subsequent 
  phyletic 
  condition. 
  Hence 
  it 
  is 
  inferred 
  

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