In any memorandum of mortgage and in any memorandum of transfer of mortgage where there are more mortgagees or transferees than 1, any implied covenant with them shall be deemed to be a covenant with them jointly in equity as well as at law, unless the amount secured is expressed to be secured to them in shares or distinct sums, in which latter case the implied covenant with them shall be deemed to be a covenant with each severally in respect of the share or distinct sum secured to him or her.