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NGC3351 (M95) is an SBb(r)II galaxy located in the Leo I group, which itself contains the closest normal elliptical galaxies. Distances to the galaxies in the Leo I group have been estimated using several secondary techniques including the Tully-Fisher relation (Aaronson $\&$ Mould, 1983, ApJ 265, 1), surface brightness fluctuations (eg. Tonry 1991, ApJ, 373, L1), the D${n}$-$\sigma$ relation (Lynden-Bell et al. 1988, ApJ 326, 19) and the planetary nebula luminosity function technique (Ciardullo, Jacoby $\&$ Ford 1989, ApJ 344, 715). Determination of the distance to this early-type galaxy using a primary indicator such as the Cepheid variable period$-$luminosity relation thus provides a powerful way of calibrating directly these secondary methods for refining the distance scale. For this reason, NGC 3351, was placed on the target list for the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale.
The HST observing sequence for NGC3351, spanning 2 months and incorporating 12 separate visits, has recently been completed. Twelve F555W (V) and 4 F814 (I) cosmic-ray split images were obtained. The F555W images show a strikingly detailed dust structure which masks the regularities seen at lower resolution along the spiral arms of this galaxy. In this paper we give a first report of the detection of Cepheid variables in NGC3351. The brightest Cepheids appear at visual magnitude 24, and periods in the sample to date range from 12 to 51 days. A sample of light curves will be presented, in addition to the V and I period$-$luminosity relations. We shall discuss the prospects for using these new data for calibrating the secondary distance indicators.
