PTEROPODA. 295 



360,000 of these microscopic suckers upon the head 

 of one Clio an apparatus for prehension perhaps 

 unparalleled in the animal creation. When not in 

 use, the appendages referred to are withdrawn and 

 concealed by two hood-like expansions that com- 

 pletely cover and protect the wliole of this delicate 

 mechanism. 



The Limacina helicina (Fig. 28) is another species 

 found in company with the above, in even still more 

 innumerable hosts. It does not materially differ 

 from the Clio in its general structure, but its body 

 is enclosed in a transparent spiral shell of exquisite 

 delicacy. This beautiful little Pteropod uses its 

 shell as a boat, and by means of its wing-like fins 

 rows itself about on the surface of the water. 



The Hyalsea (Fig. 236) is an inhabitant of warmer 



FIG. 236. GLASS SHELLS (a. HyalcecL tridentata ; 6. Cleodora pyramidata). 



regions ; its shell is somewhat like that of a bivalve 

 without a hinge, the hinder part being consolidated 

 and armed with three spines. At the sides are narrow 

 fissures, through which membranous expansions are 

 protruded, resembling those of the Clio. 



The Cleodora (Fig. 236) is another exceedingly deli- 

 cate and beautiful example. The shell of this little 

 creature is of glass-like transparency, very fragile 

 and somewhat in the form of a triangular pyramid. 

 The animal in the dark is vividly luminous, and 

 presents a very striking appearance as it shines 

 through its pellucid lantern. 



" The Pteropods," says Mr. Godwin Austen, " are 



