The flowers in the image above are those of Leucojum aestivum,the Loddon lily or summer snowflake. This is a plant with lots of name problems. In much of the American South they are called snowdrops. And then there is the book name "summer snowflake". The summer snowflake does not bloom in the summer, it blooms in the spring (now). But if you know a bit of Latin, you can see where that bookish name comes from: aestivum is a Latin adjective meaning "of summer". To add to the confusion, there is a related species Leucojum vernum (vernum is Latin for "of spring") which blooms not in the spring but rather in the late winter here.
The name Loddon lily, not commonly used in North America, derives from the presence of plants, perhaps native, growing along the River Loddon in England.
Notice the difference in the size of the flowers in the image above. The big one in the middle is probably the old variety 'Gravetye', aka 'Gravetye Var.' or 'Gravetye Giant'. It's unclear (to me at least) if this name was originally used for a particularly large-flowered clone or if the name originally was used for a group of large-flowered seedlings. Plants in commerce under this name are fertile and do form seeds, although I have not grown any on to see what they produce. The flower in the image was taken from a group which seemed to vary a lot in size.
The two flowers on the right of the image are what I think of as typical in size for Leucojum aestivum.
The flowers on the left are from plants which have been in the garden for decades. They were received under the name Leucojum aestivum pulchellum, but I don't believe for a minute that that 's what they are.
Unlike Leucojum vernum, Leucojum aestivum thrives mightily in this area. It's a familiar sight in old gardens in the city, and while there are no doubt ruderal plants in the area, for a plant so long in cultivation it does not seem to have jumped the garden fence often. It obviously is better adapted to garden life than to life in the wild. It's a distinct personality in our garden flora: nothing else looks like it. And it's well worth having both in the garden and as a cut flower.
The genus name is derived from the classical Greek words for white and violet. The usual pronunciation puts the stress on the syllable co, but since the o in that syllable is short, if you know the Latin rules for the placement of the stress it might seem that the stress should be on the syllable leu-. But there is a catch here: what looks like a j in this word is in fact an i treated as a glide (or semivowel). In the original Greek the syllabification of the word would have been leu-co-i-on, and since the i is short, the stress according to the Latin rules would have been on the syllable co - where it remains to this day. You'll raise some eyebrows if you pronounce it Latin style.