﻿140 
  T. 
  DAVIDSON 
  AND 
  W. 
  KING 
  ON 
  THE 
  TRIMERELLIDA 
  

  

  of 
  the 
  muscles 
  represented 
  by 
  the 
  scars 
  referred 
  to 
  would 
  seemingly 
  

   convert 
  them 
  into 
  specialized 
  adductors. 
  

  

  The 
  peculiarity 
  exhibited 
  by 
  the 
  sides 
  of 
  the 
  crescent, 
  as 
  just 
  

   noticed, 
  is 
  of 
  importance 
  in 
  our 
  present 
  inquiry, 
  inasmuch 
  as 
  it 
  cha- 
  

   racterises 
  the 
  earliest 
  genus 
  of 
  the 
  Trimerellids 
  ; 
  and 
  of 
  equal 
  import- 
  

   ance 
  is 
  the 
  fact 
  that 
  Dinobolus 
  is 
  the 
  least 
  calcareous 
  of 
  its 
  group. 
  

   This 
  genus 
  therefore 
  stands 
  out 
  not 
  only 
  as 
  an 
  initial 
  form, 
  but 
  as 
  

   indicating 
  the 
  period 
  of 
  development 
  or 
  chronogenesis 
  of 
  the 
  family. 
  

   "We 
  may 
  go 
  further, 
  and 
  assume 
  that, 
  while 
  the 
  Trimerellids 
  strongly 
  

   retain 
  many 
  of 
  the 
  leading 
  characters 
  of 
  the 
  more 
  ancient 
  family 
  

   (Lingidid<z), 
  the 
  genus 
  Dinobolus, 
  by 
  its 
  crescent, 
  discloses 
  a 
  relation- 
  

   ship 
  to 
  another 
  group 
  strongly 
  differentiated 
  by 
  its 
  myology. 
  As- 
  

   suming 
  this 
  to 
  be 
  correct, 
  we 
  shall 
  have 
  to 
  account, 
  on 
  the 
  doctrine 
  

   of 
  evolution, 
  for 
  the 
  creation* 
  of 
  the 
  Trimerellids 
  out 
  of 
  some 
  pri- 
  

   mordial 
  or 
  early 
  form 
  possessing 
  a 
  stronger 
  tendency 
  to 
  become 
  

   characterized 
  with 
  specialized 
  adductor 
  muscles, 
  situated 
  like 
  the 
  

   postadductors 
  of 
  Discina, 
  than 
  is 
  displayed 
  in 
  the 
  recent 
  Lingula 
  

   anatina. 
  There 
  is 
  no 
  improbability 
  in 
  the 
  idea 
  that 
  a 
  generalized 
  form 
  

   will 
  yet 
  be 
  discovered, 
  either 
  in 
  the 
  Cambrian 
  or 
  early 
  Cambro- 
  

   Silurian 
  rocks, 
  bringing 
  Discina 
  and 
  Lingula, 
  also 
  Obolus, 
  into 
  close 
  

   myotic 
  relationship 
  inter 
  se 
  and 
  with 
  Dinobolus. 
  Such 
  a 
  form 
  would 
  

   constitute 
  the 
  root 
  from 
  which 
  the 
  Trimerellids 
  have 
  originated. 
  

  

  "VI. 
  Physiography 
  or 
  the 
  Seas 
  tenanted 
  by 
  the 
  Trimerellids, 
  as 
  

  

  COMPARED 
  WITH 
  THAT 
  OE 
  THE 
  CAMBRIAN 
  SeAS. 
  

  

  One 
  of 
  the 
  peculiarities 
  which 
  characterize 
  the 
  Trimerellids 
  as 
  a 
  

   family, 
  in 
  comparison 
  with 
  the 
  related 
  group 
  the 
  Lingulids, 
  is 
  the 
  

   chemical 
  composition 
  of 
  their 
  shell-substance. 
  The 
  latter 
  family 
  

   comprises 
  forms 
  whose 
  valves 
  are 
  in 
  great 
  part 
  corneous 
  (consist- 
  

   ing 
  of 
  the 
  organic 
  " 
  basement 
  membrane 
  " 
  of 
  Bowerbank), 
  with 
  ad- 
  

   ditions 
  of 
  calcium 
  phosphate 
  and 
  carbonate 
  — 
  the 
  phosphate 
  being 
  

   the 
  largest 
  in 
  amount 
  ; 
  whereas 
  the 
  former 
  one 
  includes 
  essentially 
  

   calcareous 
  species. 
  

  

  These 
  differences 
  seem 
  to 
  be 
  in 
  intimate 
  relation 
  with 
  certain 
  

   physiographical 
  phenomena 
  that 
  distinguished 
  the 
  Cambrian 
  from 
  

   the 
  Cambro- 
  Silurian 
  and 
  Silurian 
  periods. 
  

  

  In 
  the 
  Cambrian 
  period, 
  and, 
  as 
  far 
  as 
  known, 
  before 
  the 
  Trime- 
  

  

  * 
  The 
  terms 
  creation 
  and 
  evolution, 
  it 
  requires 
  to 
  be 
  understood, 
  are 
  not 
  used 
  

   as 
  meaning 
  the 
  production 
  of 
  one 
  species 
  (hypothetically 
  an 
  interreproductive 
  

   group) 
  independent!?/ 
  of, 
  or 
  out 
  of 
  another, 
  in 
  the 
  second 
  case 
  effected 
  solely 
  by 
  

   extraneous 
  agencies 
  or 
  circumstances. 
  One 
  doctrine 
  is 
  unscientific 
  ; 
  the 
  other 
  is 
  

   based 
  on 
  phenomena 
  of 
  no 
  more 
  than 
  a 
  secondary 
  or 
  subsidiary 
  character. 
  Evo- 
  

   lution, 
  taking 
  it 
  to 
  be 
  exemplified 
  by 
  metagenesis 
  and 
  metastomotosis, 
  respectively 
  

   characterizing 
  the 
  Hydrozoa 
  and 
  Batrachia, 
  is 
  obviously 
  the 
  result 
  of 
  innate 
  

   formative 
  action 
  adapting 
  itself 
  to 
  extraneous 
  influences 
  or 
  conditions 
  : 
  the 
  

   cases 
  referred 
  to 
  do 
  not 
  differ 
  in 
  their 
  causation 
  from 
  the 
  great 
  progressive 
  

   mutations 
  which 
  the 
  life-system 
  of 
  our 
  planet 
  has 
  passed 
  through, 
  as 
  revealed 
  

   by 
  paleontology. 
  The 
  variations 
  produced 
  in 
  plants 
  and 
  animals 
  by 
  external 
  

   influences 
  constitute 
  a 
  highly 
  important 
  study, 
  giving 
  rise, 
  if 
  considered 
  in 
  con- 
  

   nexion 
  with 
  the 
  doctrine 
  of 
  innate 
  adaptive 
  formativity, 
  to 
  the 
  noblest 
  and 
  most- 
  

   exalted 
  conceptions 
  that 
  man 
  is 
  capable 
  of 
  forming. 
  — 
  W. 
  K. 
  

  

  