Ridge Section 91 is named after the 86 km lunar crater, Perrine, which is located on the northern hemisphere on the lunar Far Side. It lies to the east of Von Zeipel and to the northeast of the crater Klute. To the north-northwest is the smaller Gullstrand.  Perrine is an unusual formation that forms part of a chain of connected craters. The western two-thirds of the crater is overlain by the slightly smaller Perrine S, so that Perrine is crescent-shaped. The western rim of Perrine S is overlain by the still-smaller Perrine T. Perrine S has a worn outer rim, and a small central peak in the middle of the floor. The surviving rim of Perrine is worn and eroded, with the overlapping pair Perrine E and Perrine G intruding slightly into the eastern rim. A smaller crater has disrupted the southwest end of the outer rim, and a pair of small craters are attached to the northern rim. Only a small portion of the interior floor of Perrine still survives, forming a crescent-shaped surface between the outer rampart of Perrine S and the inner wall of Perrine. It is marked by a pair of tiny craterlets in the northern half.  (Some of the descriptions were obtained from wikipedia.org. Section 91 and this directory was created by Fran Ridge and Ned Haskin of The Lunascan Project).