FORMS OF SHELL IN BIVALVES. 
Tumid or Cordate when tlie valves are very con- 
vex and swollen, often being somewhat heart- 
shaped in section, as in SpJiivrium cnrneuin var. 
nucleus (Stnder), Anodonta cjjgneci var. corduta 
Rossm., etc. 
Fig. 126. — E.vample: Sphceriuni corncuin var. (Stnder), anterior end, X 2, ditch, 
laversham, Kent, collected by the late Miss Fairbrass. 
F.vlcate when the shell though somewhat reniform in shape, has 
the produced posterior end greatly liattened, and somewhat 
curved. 
Fig. 127. — Example: Um'o pkioi'^iiu \ax. platyrhitichoidca Dupiiy, right valve, 
River Yare, Bramerton Wood-end, Norwich, collected by Rev. S. Spencer Pearce, M.A. 
Truncate when the anterior or posterior 
margin of the shell, as the case may 
be, is not produced to a pointed 
end, but more or less abruptly 
terminated as in Pisldlum fontuudc 
(Drap.), Unio i)kt(trum (L.), etc. 
Fig. 128. — Exampleof a Pos- 
teriorly Truncate Bivalve. 
Pisidimn amnicum (Mull.), * 
right valve, X 2, 
Canal, Ambergate, 
Collected by Rev. H. ^Iilncs, M.A. 
Fig. 129. — E.vample of an Anteriorly Truncate Bivalve. 
Unio picto'uvi (L.), right valve, 
Helhersett Lake, near Norwich, collected by Mr. A. G. Stubbs. 
