192 THREE CRUISES OF THE “ BLAKE." 
the bathymetrical range of free-swimming animals like these. 
Argonauta (Fig. 113) has been known for a long time to be 
pelagic, while nautilus, though seen at the surface occasionally, 
is probably a deep-sea type. Spirula has been dredged from 
deep water by the “Challenger” and “Blake,” while French 
Fig. 117. — Tomopteris. 7. 
collectors have observed it swimming in numbers. at the sur- 
face in the Indian Ocean. The shells of Spirula (Fig. 114) are 
common on all tropical shores, while the shells of Argonauta 
