[1] : The Collaborative International Dictionary of English v.0.48

soft-shell \soft"-shell`\, soft-shelled \soft"-shelled`\, a.
   having a soft or fragile shell.
   1913 webster

   soft-shell clam zool., the long clam. see mya.

   soft-shelled crab. zool. see the note under crab, 1.

   soft-shelled turtle. zool. same as soft tortoise, under
      soft.
      1913 webster
see also:
soft-shell clam mya soft-shelled crab crab soft-shelled turtle soft tortoise 
soft 

[2] : WordNet (r) 2.0

soft-shelled turtle
     n : voracious aquatic turtle with a flat flexible shell covered
         by a leathery skin; can inflict painful bites syn: pancake
         turtle
see also:
pancake turtle 

Turtle >> T Words
Turtle, definition of term: Turtle
turtle_pag1.html

Turtle Grass >> T Words
Turtle Grass, definition of term: Turtle Grass
turtle+grass_pag1.html

Snapping Turtle >> S Words
Snapping Turtle, definition of term: Snapping Turtle
snapping+turtle_pag1.html

Sea Turtle >> S Words
Sea Turtle, definition of term: Sea Turtle
sea+turtle_pag1.html

Painted Turtle >> P Words
Painted Turtle, definition of term: Painted Turtle
painted+turtle_pag1.html

Box Turtle >> B Words
Box Turtle, definition of term: Box Turtle
box+turtle_pag1.html