I acquired this cover the other day -- a consequence of my newfound passion for postal history.
The stamp design (10c Daniel Webster, dark green, perf. 12) was issued as both the #258 (unwatermarked) and the #273 (watermarked (191)).
Fortunately for me, the 18Feb1895 postmark date eliminated the need to determine the presence or absence of a watermark and let me reasonably conclude that the stamp is a #258 (#273 was issued June 1895; earliest documented use 25Jul1895).
