MOLLUSCA. 473 



short way behind the anterior tentacula. Near this plume, 

 but towards the right side, is a single simple filament, like 

 a tentaculum. The anterior tentacula occupy the usual 

 position, are setaceous, and have the eyes placed^at the base 

 behind. The spiral shell is capable of containing the 

 body, and the aperture can be closed by a spirally striated 

 operculum attached to the foot. The internal structure is 

 unknown. 



B. Branchiae issuing laterally from between the cloak and 

 foot. 



This division includes the orders Cych-branchla and 

 Infero-branchia of CUVIER, which we have ventured to 

 bring together, as connected by the common character of 

 the position of the gills. 



(1.) Body protected dor sally by a shelly covering. Cyclo- 

 branchia. 



a. Shell simple. 



41. PATELLA. Shell entire. Mouth with tentacula. 



This genus differs from the others of this order. The 

 back is covered by a conical shell, within the cavity of which 

 the animal is capable of withdrawing itself. The cloak is 

 large, covering both the head and foot. It is united with 

 the shell along its superior margin. The foot is fleshy, and 

 furnished with numerous muscular filaments, which unite, 

 in the superior part of the cloak, to form a strong muscle, 

 by which the body adheres to the shell. The action of 

 this muscle brings the shell close to the surface to which 

 the foot adheres, or removes it to a distance. 



The head is furnished with a large, fleshy snout, support- 

 ing at the base two pointed tentacula. The eyes are placed 

 on a small elevation at the external base of the tentacula. 

 A little way behind the head, and below the cloak, on the 

 right side, are two apertures, being the anus and orifice of 

 generation. The gills occupy the same position as in the 



