this embodiment comprise simple friction c clamps or channel clamps the clamps may be of any convenient construction and may be attached at two or more edges of the assembly as required it will be appreciated that lid 120 may be covered with contaminants in the present invention the lid can be removed prior to removal of gasket 116 in a hood in those embodiments in which gasket 116 is bonded to the thermal sheet 92 that is wells 112 will still be covered when lid 120 is removed by virtue of thermal sheet 92 not shown in fig5 overlying the corresponding opening in gaskets 116 referring now to fig6 of the drawings in an alternative embodiment resilient gasket 128 has a plurality of openings 130 in alignment with wells 112 the arrangement of openings 130 in resilient gasket 128 is best shown in fig6 a in this embodiment openings 130 have a slightly smaller diameter than the openings of wells 112 which contributes to confinement of samples within wells 112 to prevent cross contamination it will be appreciated that by providing openings 130 in gasket 128 reagents can be easily added to wells 112 simply by removing clamps 124 and lid 120 from assembly 100 the lid and clamps can then be replaced to close and seal wells 112 alternatively where the gasket does not have any openings therein it may be formed of a self sealing material such that reagents can be added by way of a syringe or the like referring now to fig7 of the drawings a multi.