arheyman's Identifications

A sea snail with sharp conical shape like a pointy hat. Base appears round when viewed from the top, looking down.

Update 12-9-21:
Nassarius fossatus a.k.a. Channeled Basket Snail, Channeled Dog Whelk, Giant Western Nassa. Can get up to 5cm (2"). Carnivorous snail that drills holes into living clams and other snail shells to feed on their inner tissues.

Beachcombers's Guide to Seashore Life of California, J.D. Sept, Rev. ed. 2009, p. 104.

https://seanet.stanford.edu/Prosobranchs#Caesia