The Kar 98 (not to be confused with earlier cavalry carbines) was actually a short rifle, comparable to the British SMLE and the U.S. M1903. The Germans apparently intended to replace all their long Gew. 98's with the Kar. 98 (aka Kar. 98a), but WWI ended before they did so. Many Kar. 98's were made, mainly at Erfurt, the Imperial government arsenal, and after the war, a large quantity were sold to Turkey, as a result of which they have become known to collectors as "small ring Turks." (Turkey never made Mauser receivers, though they reworked and rebarrelled many.)
Other than the size of the receiver ring, the receivers are standard 1898. The Fraktur marking on the left side appears to read "Kax 98", to the confusion of some collectors.