pete: A small hint: It is important to see the actual shape and this is easiest if you take the photo from the exact horizontal position, not even the slightest downwards or upwards. If you look at the red vase picture in the link from Wayne you see the point!
Wayne has it totally correct.
I agree both Riihim√§ki and Riihim√§en are in this sense correct as people know they both mean the same factory. Just a curiosity to enlighten the fact: Finnish language does not use prepositions but bend the word for a genitive case to express possession, so "Riihim√§en Lasi" means "Riihimaki's Glass"
scavo: 1465 would be mold blown, turned. The distictive ridges in the base develop somehow in the process of annealing and cooling.
The last hand made blown glass items were made in the end of year 1976 in RL. Tamara Aladin designed about 150 known designs but a huge number more that were not documented or sold as her designs. (probably the most of the large export range from the end 60's until 1976. Btw: 1374 is one of those designer is not known, also 1371)
Cannot say anything about your 151?, why not add a thread with a photo?