a multiple filter media assembly constructed in accordance with the present invention is illustrated in fig1 and 2 and includes a generally rectangular metal frame , indicated generally at 20 , for permanently mounting one or more layers of a particulate filter media 22 . preferably , the filter media 22 comprises a plurality of layers of expanded metal which form a long - lasting , re - usable particulate filter . the construction of frame 20 and media 22 are old and well - known in the trade and have been used for many particulate filter applications . one typical application for such filters is in range hoods for the removal of grease aeresol generated while cooking . since the frame is a relatively costly item , such a frame and filter construction may be removed , cleaned and reused many times . however if the filter is damaged or otherwise becomes unusable , the frame and filter must be replaced because of the permanent nature of the construction . in applications wherein it was desired to also include gaseous filter media for odor removal , the prior art employed a combination of particulate and gaseous filter media permanently mounted in the same frame . however , this type of construction is less satisfactory as the gaseous media possesses a significantly shorter useful life than the particulate media . therefore , the user is left without effective odor removal or must replace the total filter assembly , including the expensive frame and particulate media . in accordance with the present invention , permanent frame 20 is provided with a plurality of retaining members , indicated generally at 24 , which form an auxillary filter media retaining means . retaining members 24 comprise a strip of resilient material , preferably spring steel for example , which is pre - formed into a predetermined configuration such as shown in fig1 and 2 . frame 20 is normally formed by a conventional bending method wherein top , bottom and rear walls are created along fold lines joining the top and bottom walls to the rear wall . the top and bottom walls 26 are also provided with an inwardly turned lip 30 , which upon assembly , forcefully engage the edges of the layers of particulate filter media 22 which is positioned within a channel 32 formed between the walls 26 and 28 of frame 20 . in the manufacture of a conventional frame 20 , bottom wall 26 and rear wall 28 are formed essentially as shown , however , top wall 26 is only partially bent downwardly toward the final position shown in fig2 . at this point of the conventional assembly method , the outer edges of layer 22 of the particulate filter media are positioned within channel 32 . the conventional assembly is then completed by a conventional bending press apparatus which closes top wall 26 to its final position wherein the layer 22 of particulate filter media is engaged and held between the lips 30 provided on top and bottom walls 28 . however , in accordance with the present invention , a retaining member 24 , which preferably comprises a strong resilient strip of material , is inserted with its rear portion 25 disposcd within a channel 32 prior to closing top wall 26 with the outer finger portion 27 extending outwardly from frame 20 over the upper surface of layer 22 . the members 24 are preformed and dimensioned proportionally to the dimension of frame 20 such that lip 30 on the top wall 26 will enter a recess 29 in member 24 upon closing top wall 26 to the final assembled position as shown in fig1 and 2 . in addition to fixing the edges of layers 22 within channel 32 of frame 20 , this procedure also secures each retaining member 24 within the respective channels 32 along each side of frame 20 and biases the concave curvature of finger portion 27 into engagement with the upper surface of layer 22 . with members 24 assembled as described herein , a layer of gaseous filter media 34 of proper dimensions may be easily positioned in overlying relationship with layer 22 by sliding an edge thereof under the finger 27 of member 24 . this is accomplished by slightly raising the outer end of finger 27 to provide clearance to position the layer 34 flat over the surface of layer 22 with the outer edges of layer 34 generally coinciding with the inner edge of frame 20 . gaseous filter media layer 34 typically may comprise a non - woven sheet of synthetic fibers or expanded and slit paper filter media which may be impregnated with activated charcoal for odor , aeresol and further particulates removal . when removal of layer 34 is required , a similar lifting of finger 27 permits layer 34 to be easily pulled from under fingers 27 and discarded . a replacement layer 34 may then be positioned as described above to provide a new efficient gaseous filter layer . prior to replacirg layer 34 , particulate layer 22 may be cleaned , if needed , by washing with soap and water . then the whole filter assembly may be returned to its original condition for efficient operation . typically , the particulate filter will outlast several replacement gaseous filters before replacement of the frame and media layer 22 is required . in the preferred embodiment shown , the outer end of finger 27 is provided with a tooth or barb 31 to enhance the engagement between the fingers 27 and the removably mounted layer 34 . now referring to the embodiment shown in fig3 and 4 , a modified retaining member 24 - a is illustrated . the remaining components of the filter assembly 20 - a are identical to those shown in fig1 and 2 and therefore are indicated by the identical reference numerals . the modified retaining member 24 - a comprises a strip of metal which has significantly less inherent resiliency as compared to member 24 . therefore it may be raised or lowered between unbiased open and closed positions by vertical movement beyond its elastic limit . member 24 - a is pre - formed to assume the configuration shown in fig3 and 4 and includes an inner portion 25 - a which is inserted into channel 32 , an outer finger portion 27 - a and a recess 29 - a . member 24 - a is assembled within frame 20 - a in the same manner as previously described relative to member 24 . lip 30 of top wall 26 is similarly inserted into engagement with the bottom of recess 29 - a to force it into engagement with the media layer 22 also assembled in channel 32 . lip 30 of top wall 26 also anchors retaining member 24 - a such that it may be bent upwardly or downwardly along the outer raised edge of recess 29 - a . the nature of the metal strip forming member 24 - a is by design easily bent beyond its elastic limit to an open position or a closed position into engagement with a media layer 34 positioned over the surface of layer 22 such as best seen in fig3 . the finger portion 27 - a also has a modified configuration in view of its operation and includes a downturned lip 36 which is serrated to more firmly grip layer 34 when finger 27 - a is closed down upon layer 34 . the nature of the construction of member 24 - a makes it somewhat easier to replace a new layer 34 as compared to member 24 in that the finger 27 - a may be raised to an stable position providing more clearance to properly place layer 34 in its operative position overlying layer 22 . however , finger 27 - a will not automatically engage layer 34 and must be manually bent downwardly and pressed into engagement with layer 34 to fix layer 34 in the assembly . in view of the foregoing description , it should be understood that the filter assembly of the present invention provides a significant improvement over the prior art by providing an efficient and cost effective unitary construction having both a permanently framed filter media and a removably mounted filter media which operates in a simple and relatively easy manner .