There are a few reasons they may not come up. Something eating them is certainly one possibility. How deep did you plant them? Did you give them a thorough watering after planting? They need to be well watered after planting to promote root growth. Were they planted in an area with poor drainage? They may have rotted. Fritillaria don't like to dry out, but neither do they like soggy soil. Hope this helps out. Good luck and have fun planting. Be sure to work lots of organic matter into the soil before planting.

Did you plant them early enough? I don't know about snowdrops, but after next week it will probably be too late for frits.