3«0 
THE OCEAN WORLD. 
The animal which lives in this elegant dwelling has the form °1' 
an elongated cylinder. Its mantle is closed in its whole length 
and only open at the ends at one side for the passage of the food) 
and at the other for the passage of a tube formed of two syphon® 
united together. This curious shell, the various species of which are 
represented in Pl. XIX., are known as razor-fish, sabre-fish, and other 
names, which in some respects indicate the peculiar form of the shell' 
In the Pholadm we have a family which not only bury themselves 
Fig. 153. Pliolades daotylus, havlug hollowed out a shelter In a block of gneiss. 
in the sand, like the Solens and then - congeners, hut they are able in 
some mysterious way to excavate for themselves a dwelling in argil' 
laceous rocks, and even in harder stone. The engraving represents P' 
dactylus, which has hollowed itself a home out of a block of gneiss 
This dwelling is a cell just deep enough to contain the animal and i fe 
shell, as represented in Fig. 173. To excavate its cell at the bottom 
of one of these gloomy retreats seems to be all that the animal lives for- 
To ascend to the summit or sink to the bottom of their narrow dorm er 
window makes up all the accidents of existence to these strange creatures , 
