﻿1018 
  Forty-seventh 
  Report 
  on 
  the 
  State 
  Museum, 
  

  

  Protorhyncha, 
  Hall. 
  1893. 
  

   (P)ate 
  42, 
  figs. 
  4-6.) 
  

  

  Shells 
  biconvex, 
  with 
  a 
  low, 
  ill-defined 
  fold 
  and 
  sinus 
  on 
  

   brachial 
  and 
  pedicle- 
  valves 
  respectively. 
  Pedicle- 
  valve 
  with 
  a 
  

   false 
  cardinal 
  area 
  defined 
  by 
  ridges 
  diverging 
  from 
  the 
  beak. 
  

   Pedicle-passage 
  triangular, 
  rarely 
  showing 
  any 
  trace 
  of 
  deltidial 
  

   plates. 
  Teeth 
  very 
  small, 
  supported 
  by 
  thin 
  lamellae 
  which 
  rest 
  

   upon 
  the 
  bottom 
  of 
  the 
  valve 
  and 
  are 
  not 
  adnascent 
  to 
  the 
  

   lateral 
  walls 
  of 
  the 
  shell. 
  In 
  the 
  brachial 
  valve 
  the 
  dental 
  

   sockets 
  are 
  small 
  ; 
  the 
  hinge-plate 
  consists 
  of 
  two 
  minute 
  dis- 
  

   crete 
  processes, 
  the 
  surfaces 
  of 
  which 
  are 
  slightly 
  inclined 
  toward 
  

   each 
  other. 
  These 
  were 
  the 
  bases 
  of 
  the 
  brachial 
  supports 
  

   but 
  show 
  no 
  points 
  of 
  attachment 
  to 
  the 
  crura 
  ; 
  they 
  are 
  

   separated 
  by 
  a 
  triangular 
  incision 
  extending 
  to 
  the 
  bottom 
  of 
  the 
  

   valve. 
  There 
  is 
  no 
  cardinal 
  process 
  nor 
  median 
  septum 
  in 
  the 
  

   brachial 
  valve, 
  and 
  no 
  trace 
  of 
  muscular 
  scars 
  iu 
  either 
  valve. 
  

  

  Type, 
  Protorhyncha 
  dubia, 
  Hall. 
  Chazy 
  limestone. 
  

  

  Distribution. 
  Lower 
  Silurian. 
  

  

  Orthorhynchula, 
  Hall. 
  1893. 
  

   (Plate 
  42, 
  figs. 
  7-10.) 
  

  

  Shells 
  rhynchonelloid 
  in 
  contour; 
  hinge-line 
  short, 
  straight, 
  

   extending 
  for 
  about 
  one-third 
  the 
  transverse 
  diameter 
  of 
  the 
  

   valves. 
  A 
  true 
  cardinal 
  area 
  is 
  present 
  on 
  both 
  valves, 
  that 
  of 
  the 
  

   pedicle-valve 
  being 
  considerably 
  the 
  broader, 
  erect, 
  often 
  incurved. 
  

   Each 
  valve 
  also 
  possesses 
  a 
  distinct 
  triangular 
  delthyrium, 
  that 
  of 
  

   the 
  pedicle-valve, 
  according 
  to 
  the 
  evidence 
  at 
  hand, 
  never 
  being 
  

   in 
  any 
  degree 
  closed 
  by 
  deltidial 
  plates. 
  External 
  surface 
  

   strongly 
  and 
  simply 
  plicated, 
  the 
  median 
  fold 
  and 
  sinus 
  being 
  

   well 
  developed. 
  On 
  the 
  interior, 
  the 
  pedicle-valve 
  possesses 
  

   blunt 
  teeth 
  which 
  rest 
  upon 
  the 
  laterally 
  thickened 
  walls 
  of 
  the 
  

   valve 
  and 
  are 
  not 
  supported 
  by 
  lamellae. 
  Between, 
  and 
  slightly 
  

   in 
  front 
  of 
  these 
  lies 
  a 
  short, 
  subquadrate 
  muscular 
  scar. 
  The 
  

   brachial 
  valve 
  possesses 
  a 
  linear 
  cardinal 
  process, 
  on 
  either 
  side 
  

   of 
  which 
  are 
  two 
  discrete 
  crural 
  plates, 
  sharply 
  concave 
  on 
  the 
  

   upper 
  surface 
  and 
  diverging 
  anteriorly 
  for 
  a 
  considerable 
  

   distance. 
  

  

  Shell-substance 
  fibrous, 
  impunctate. 
  

  

  Type, 
  Orthorhynchula 
  Zi?meyi, 
  JSTettelroth 
  (sp.). 
  

  

  Distribution. 
  Lower 
  Silurian 
  (Hudson 
  Kiver 
  group). 
  

  

  76 
  

  

  