Spirula spirula (Linnaeus, 1758) ; Spirulidae; 1. a) portions of the shell exposed in front and behind b) the funnel or siphuncle 2. side view of the shell 3. Shell insections to show partitions or septa
Date 1901
Source A Guide to the shell and starfish galleries of the British Museum p.49
Author British Museum
Source: https://commons.wikimedia.org/wiki/File:Spirula_spirula_001.png

The ram's horn squid, little post horn squid or tail-light squid (Spirula spirula) is a species of deep-water squid-like cephalopod mollusk. It is a deep-ocean dweller. The shell of Spirula is extremely light in weight, very buoyant, and surprisingly durable; it very commonly floats ashore onto tropical beaches all over the world. This seashell is known to shell collectors as the ram's horn shell or simply as Spirula.