140 UNIVALVES. 



has much the appearance of being composed of 

 two pieces united by the keel, and seems to be 

 the link between the univalve and bivalve 

 shells. 



OBSERVATIONS ON THE SHELL AND ITS 

 INHABITANT. 



The animal inhabiting these elegant shells is 

 soft and fleshy, and has a large portion of its 

 body enveloped in the mantle ; its head is 

 furnished with two eyes, and round its mouth 

 are arranged like rays eight elongated and 

 pointed tentacula or arms. Two of these have a 

 thin membrane extending more than half their 

 length. This singular appendage the animal 

 can expand or draw in at pleasure. The shell 

 is of a thin paperlike substance, resembling in 

 form a kind of boat. Few objects can be con- 

 ceived more interesting than this beautiful animal 

 seated in its pearly little vessel : two tentacula 

 erected with their membrane unfurled like 

 a sail, whilst the remaining six, suspended over 

 the sides of the little bark, perform the office of 

 oars. When wafted by propitious gales, it 

 calmly rides over the waves : but should a storm 

 threaten, or an enemy approach, it precipitately 

 hauls in its tackle, shrinks into its shell, and 

 drawing in water to add to its weight, seeks 

 protection in the depths of the sea : the danger 

 over, it diminishes the gravity of its shell by eject- 

 ing the water, and rises again to the surface. 



