SUMIF problem

I am having a hard time writing this formula. I have two sheets in my xls book. In sheet one I have two relavent columns
1) shape name and 2) sum of assays

in sheet two I have two other relavent columns
1)shape name and 2)assay value

I am trying to write a formula that populates 'sum of assays' by matching sheet1 shape name to sheet2 shape name and then summing all of the relevant assay values associated with that particular shape.

I sheet1 I have many different shape names and in sheet 2 I have multiple assays for each shape name. So I am trying to automate this instead of having to sum by hand each one. Any advice would be great! Thanks!

Thank you so much, worked just right