This is a Packard lightbulb sporting a Thomson-Houston base, a base which became popular in the 1890's. Thomson-Houston based bulbs are not super easy to find, but they aren't that rare either. There are many different variations of the Thomson-Houston base; there's even one that is made entirely of porcelain. Most T-H bulbs are 100+ years old, but some were made after the year 1900, especially those of the full porcelain-based variety. Some of these use cement (instead of plaster) to hold the bulb to the base, which indicates post-1900 manufacture. When the 20th century arrived, many homes still had their old T-H sockets in place. (in 1900, 10% of all sockets in use were Thomson-Houston sockets). But TH-Edison adapters were soon made, enabling TH sockets to hold Edison bulbs, and this soon led to the abandonment of the T-H base altogether.
My Packard bulb has an intact filament, however it has no continuity (electricity does now flow through it). I find that very strange because this lightbulb shows clear signs of having been used for many hours before it lost its continuity (darkened glass). This is why there's no picture of it lit too! How do I know that this is a bulb made by Packard? There's a Packard label on the inside of the base. This bulb is held together to its base with plaster, and is insulated at the bottom with porcelain.
Thomson-Houston bases look much larger in pictures than they really are. Someone who has never seen one in person may think that they are as large as a mogul base, but they're not. Actually, they are slightly larger than a regular Edison base. The neatest thing about TH bases is that the bulbs can be displayed very easily, since they can stand upright!