﻿SONNINIA 
  AND 
  HAMMATOCEEAS. 
  

  

  661 
  

  

  ordinary 
  resemblance 
  to 
  the 
  species 
  in 
  the 
  zone 
  of 
  which 
  it 
  occurs, 
  

   namely, 
  Lioceras 
  concavum. 
  

  

  This 
  is 
  what 
  may 
  be 
  called 
  convergence 
  (in 
  outward 
  shape) 
  of 
  the 
  

   ultimate 
  changes 
  — 
  in 
  other 
  words, 
  senile 
  convergence. 
  

  

  Conclusions. 
  

   is 
  remote 
  from 
  Sonninia 
  

  

  by 
  descent, 
  in 
  spite 
  

  

  1 
  . 
  Hammatoceras 
  

   of 
  outward 
  similarity. 
  

  

  2. 
  It 
  is 
  descended 
  from 
  Deroceras 
  and 
  is 
  therefore 
  allied 
  to 
  — 
  is 
  a 
  

   cousin 
  of 
  — 
  Stephanoceras. 
  

  

  3. 
  The 
  inclusion 
  of 
  Hammatoceras, 
  Sonninia, 
  and 
  the 
  Hildo- 
  

   ceratidse 
  in 
  one 
  genus 
  Harpoceras, 
  merely 
  because 
  they 
  possessed 
  a 
  

   carina, 
  was 
  most 
  unnatural. 
  

  

  It 
  may 
  be 
  interesting 
  to 
  note 
  that 
  the 
  following 
  have 
  been 
  identi- 
  

   fied 
  among 
  the 
  species 
  of 
  Hammatoceras 
  which 
  occur 
  in 
  England 
  : 
  — 
  

  

  ^> 
  

  

  <D 
  

  

  o 
  

  

  

  

  O 
  

  

  

  SI 
  

  

  w 
  

  

  

  

  §5 
  

  

  o 
  

  

  55 
  

  

  

  SS 
  

  

  K5J 
  

  

  

  

  53 
  

  

  

  cT 
  

  

  ^ 
  

  

  Hamm. 
  insigne 
  (Schubler) 
  

  

  - 
  snbiusigne 
  ( 
  Oppel 
  £f 
  Dumortier) 
  

  

  Alleoni 
  {Bum.) 
  

  

  Sieboldi 
  {Oppel) 
  

  

  dolium, 
  n. 
  sp 
  

  

  allobrogense, 
  mutation 
  of 
  

  

  planinsigne 
  {Vacek) 
  

  

  clirnacompkaluni 
  ( 
  Vacek) 
  

  

  arnaltheiforaie 
  ( 
  Vacek) 
  

  

  amplectens, 
  n. 
  sp 
  

  

  Descriptions 
  of 
  Neiv 
  Species. 
  

  

  Hamhatoceeas 
  dolitjm, 
  n. 
  sp. 
  (PI. 
  XXII. 
  figs. 
  17, 
  18.) 
  

  

  1886. 
  Hammatoceras 
  subinsigne, 
  Vacek 
  (non 
  Oppel 
  & 
  Dumortier), 
  

   f 
  ' 
  Oolithe 
  Cap 
  S. 
  Yigilio," 
  Abh. 
  k.-k. 
  geol. 
  Eeichsanstalt, 
  Bd. 
  xii. 
  

   pi. 
  xiv. 
  figs. 
  1-4. 
  

  

  Discoidal, 
  somewhat 
  compressed, 
  hollow-carinate. 
  Whorls 
  ellip- 
  

   tical 
  to 
  subquadrate, 
  ornamented 
  with 
  spines 
  — 
  placed 
  almost 
  upon 
  

   the 
  middle 
  of 
  the 
  whorl 
  — 
  from 
  which 
  coarse 
  ribs 
  proceed, 
  generally 
  

   in 
  triplets, 
  to 
  meet 
  the 
  carina 
  at 
  right 
  angles, 
  and 
  these 
  ribs 
  are, 
  

   practically, 
  persistent 
  up 
  to 
  the 
  carina. 
  The 
  part 
  of 
  the 
  whorl 
  inside 
  

   the 
  spines 
  is 
  smooth, 
  possessing 
  a 
  series 
  of 
  small 
  undulations 
  opposite 
  

   the 
  spines. 
  Ventral 
  area 
  not 
  defined. 
  Carina 
  not 
  large, 
  distinct, 
  

   hollow. 
  Inclusion 
  up 
  to 
  the 
  spines 
  ; 
  umbilicus 
  open 
  and 
  ornamented 
  

   with 
  spines 
  almost 
  to 
  the 
  centre. 
  As 
  the 
  species 
  advances 
  towards 
  

   adolescence 
  the 
  spines 
  give 
  place 
  to 
  elongate, 
  coarse, 
  primary 
  ribs, 
  

  

  