Sedlex installed by opam but not found by ocamlfind

   Here is my problem : spam tells me that sedlex is installed, but ocamlfind cannot find it ;

MacBook-Pro-de-Ewan:Diasur ewan$ opam list
# Installed packages for system:
base-bigarray                 base  Bigarray library distributed with the OCaml compiler
base-threads                  base  Threads library distributed with the OCaml compiler
base-unix                     base  Unix library distributed with the OCaml compiler
camlp4               4.02.1+system  Camlp4 is a system for writing extensible parsers for programming languages
oasis                        0.4.5  Architecture for building OCaml libraries and applications
ocaml-data-notation         0.0.11  Store data using OCaml notation
ocamlfind                    1.5.5  A library manager for OCaml
ocamlify                     0.0.1  Include files in OCaml code
ocamlmod                     0.0.7  Generate OCaml modules from source files
ppx_tools                   0.99.2  Tools for authors of ppx rewriters and other syntactic tools
sedlex                      1.99.2  unicode-friendly lexer generator (successor of ulex, now based on -ppx inst
type_conv                112.01.01  Library for building type-driven syntax extensions
MacBook-Pro-de-Ewan:Diasur ewan$ ocamlfind ocamlc -c -package sedlex fowl.ml
ocamlfind: Package `sedlex' not found