Trev, I don't know the name of the pattern. I've seen it referred to elsewhere on the web as 'Wreath'.
Nor do I know for sure what year it was introduced. But there's reason to think it was between the early 1850s and the early 1860s, because of its strong resemblance to other patterns popular then.
NYC: 'Jenny Lind', produced by Albert Coles in the early 1850s, was very popular. A version of 'Jenny Lind' even more similar to the Seymour pattern was made by Gale & Willis, with the inward notch above a circular bulge; the Gale & Willis working partnership was from 1859-62.
Philo Gilbert's variation on the popular 'Olive' pattern, patented in 1859, included a wreath motif.
And Francis Gibney patented a pattern in 1862, called 'Gibney' when Whiting acquired and produced it, that had the same oval-over-circle shape.
Syracuse, NY: Another pattern in the Jenny Lind family is 'Laurel', by Bunnell & Schreuder, who had a partnership 1853-57 in Syracuse, where Seymour worked. Notice how similar the style of the drop is to the Seymour pattern.
Philadelphia: Taylor & Lawrie produced pieces in the 'T&L pattern' (some marked with those exact words) for Bailey & Co. between 1846 and 1857 at the latest. The shape is strikingly similar, but I'm not sure how much exposure Seymour and other upstate New York producers would have had to the T&L pattern.
On the other hand, Seymour worked well beyond the early 1860s, at least until 1870. The oval-over-circle shape of this pattern had a final resurgence when J.R.Wendt in New York City, selling through Ball, Black & Co., brought out (and patented) the very Gibney-like 'Union' in 1865. 'Union's popularity (in northern markets, at least) might have inspired Seymour to try to take advantage of the enthusiasm with his 'Wreath'. I'd even be inclined to interpret the wreath motif as victory laurels if not for the prominent central flower, which does make the design much more evocative of a bridal wreath.
But the real fashion for this shape was earlier. By the late 1860s, as the pace of new pattern introductions picked up, my guess is that the shape would have begun to look pretty played out. So, best guess: 1852-1865. Does that help?
.
