stage of turbine blades 20 only one of which is shown the stage of blades 20 is surrounded by a ring of shroud segments 22 which in a non operative mode of engine 10 are very closely spaced from the tips 24 of respective blades 20 the spacing is achieved by supporting the shroud segments by cooperating hooked features 26 and 27 on their leading edges and on the interior of a flexible casing 28 and by u2018 birdmouth u2019 joints 30 on the interior of flexible casing 28 cooperating with spigots 32 on the trailing edges of the shroud segments 22 although in this particular case a u2018 birdmouth u2019 joint 30 is employed other fastening devices such as hooks could be employed likewise the spigots 32 could be replaced by an alternative fastening device such as a hook or lip casing 28 is fixed in its upstream end it to further casing structure 34 which extends towards or over the combustion zone 14 the downstream and of casing 28 is supported on further fixed structure 36 via a sliding u2018 bird mouth u2019 joint 38 which enables some axial movement thereof through casing 28 flexing during operation of engine 10 again although a u2018 bird mouth u2019 joint 38 is employed other suitable joint arrangements which provide the necessary degree of sealing may be used casing 28 has a number of struts of substantial proportions projecting radially therefrom in equi angularly spaced array the outer ends of which.