GASTEROPODES. 269 



hue below. While crawling up the side of the vessel, its form was well 

 displayed : the tentacula, with a fold or hollow in the upper part, 

 much resembling a horse's ear : the cornicula, rising erect from the neck, 

 with the black eye near the base, and the cavity of the back open or 

 closed, or surrounded by its protecting membrane. This animal extended 

 just two inches. It afforded satisfactory delineations, from which its form 

 and appearance are rendered very explicit. 



In another fine and healthy specimen, of about equal dimensions, or 

 rather larger, the black eye was surrounded by a white line. 



This animal was quite vigorous, and fed copiously on the common 

 green fucus. But I know not that such food was the most congenial, for 

 it did not undergo much alteration by digestion. The creature's body 

 was very transparent. 



This specimen always testified a disposition to rise to the surface of 

 the water, where it swam supine ; or it would adhere by the tip of the 

 tail to some solid substance, or to the glass, suspending itself in the water. 

 It is a distinguishing habit of the Aplysia to suspend itself in this manner. 



A third specimen, towards the same size as the others, was very 

 beautiful : the skin sparingly strewed with white specks, the animal 

 plump and vigorous. I rate these animals as nearly equal, for they ex- 

 tended twenty-four, twenty-five, and twenty-six lines respectively. 



White specks were also on the body of a smaller specimen, which fed 

 copiously on some of the Florideae, and increased rapidly in size. Indeed, 

 the colour of the species seems to indicate that the natural food is to be 

 sought among algae of that description. This animal survived ten months ; 

 it died suddenly, tinging the water purple. Sometimes a great quantity 

 of water is so tinged by a single living specimen. 



None are easily preserved permanently. 



PLATE XXXVII. 



FIG. I. Aplysia depilans, profile. 



2. Upper surface. 



3. Under surface. Tentacula, a. Cornicula, b. Branchial cavity sur- 



rounded by its protecting membrane, with a smooth purple mar- 

 gin, c. 



