110 The Official Guide to the — 
fish, Squid, Spirula, and Paper Nautilus, and is so- 
named from its members possessing two gills. The 
shuttle-shaped mass is the internal shell or “bone” 
of the Cuttle-fish (Sefza officinalis), a ‘common object 
of the sea shore;” it is the most substantial form of 
“shell” possessed by this order; in the Octopus, 
there is no such support; and in the Calamaries it is 
represented by a translucent horny substance which, 
from its fancied resemblance in shape to the quill and 
plume of a goose feather, is called the “pen.” ‘The ~ 
curious coiled, many chambered shells resembling 
“Post-horns” belong to a cuttle-fish of the genus 
Spirula ; these were long a puzzle to “‘ Conchologists,” 
for although very abundant on the shores of New 
Zealand, and even occasionally borne by the Gulf 
Stream to Tenby, S. Wales, on our own coast, the 
animal of which they formed a part was unknown — 
in its perfect state till 1878, when Professor Owen 
had the opportunity of dissecting a complete specimen 
and dispelled the mystery. : 
The delicately beautiful “ Argonaut” or Paper Nau- 
tilus, is the only species of the order which has an 
external shell, and yet although formed by it, is not 
attached to the animal which inhabits it, and 1s, more- 
over, peculiar to the female sex; it is now known that ~ 
the female inhabits the shell which she builds for 
herself, and uses chiefly as a receptacle for the safe 
keeping of her eggs. 
Another very remarkable Mollusc, with which also” 
the name of Professor Owen will always be associated, 
is the Pearly Nautilus (Wautilus pompilius), an inhabi- 
tant of the tropical seas of China, India, and the 
Persian Gulf. This species is the only existing 
member of the once numerous order TETRA- 
BRANCHIATA, or four-gilled Molluscs, of which 
more than 1,600 fossil species are known belonging 
