./assemblyDB.116.las
test.sh: line 9: ${ls $filename | sed 's/assemblyDB.//' | sed 's/.las//'}: bad substitution

for filename in $(find . -type f -name "assemblyDB.*.las"); do
   echo $filename
   no=${ls $filename | sed 's/assemblyDB.//' | sed 's/.las//'}
   echo $no
done

no=${filename/assemblyDB.}   # remove first match
no=${no/.las}

no=${filename#assemblyDB.}   # remove from start of string
no=${no%.las}                # remove from end of string

shopt -s globstar         # in Bash
for filename in **/assemblyDB.*.las; do
    ...