Interesting nice mix. Few comments:
1) I agree with Ariel. This is not a Shibriya. The blade shape and cross section, The handle shape, the style of decoration and the style of connection to the belt are all very different from what I am familiar with the Jordanian / Palestinian Shibriya. A Saudi Shibria?? I am not familiar with this.
2) Blade: The shallow diamond cross section is not common in the Jordanian Palestinian ones and also I think it is not very common in other Saudi / Yemenite daggers / Khanjars . For this shape of cross section I would look more North – East of the Arab peninsula: Iraq, Persia and even further east. It may be worth to check the quality of the steel.
3) As Stu noted, There is a big difference in style and decoration technique in the two parts of the scabbard. The lower part, between the locket and the tip of the scabbard is engraved in a very poor technology, very common to decoration technique and style found in Jordan, Palestine and sometimes Syria. But the tip with the double twisted silver wire is again different. Also may be coming from further north east. The silver tail at the tip of the scabbard is probably a later addition as well.
4) I therefore think that it is a mix of parts collected from various sources to make a dagger.
5) For somewhat similar shape and size daggers, but of far better quality see the fierce discussion in:
http://www.vikingsword.com/vb/showth...afghan+khanjar