ANIMALIA MOLLUSCA. i) 
have almost always a distinct head before. We call these 
the GASTEROPODA. 
A fourth class is composed of those where the mouth remains 
hidden in the bottom of the mantle, which also encloses the 
branchiz and viscera, and is open either throughout its 
length, at both ends, or at one extremity only. Such are our 
ACEPHALA. 
A fifth comprises those which, also inclosed in a mantle, 
and without an apparent head, have fleshy or membranaceous 
arms, furnished with cilia of the same nature. We term these 
BRACHIOPODA. 
Finally, there are some which, although similar to the other 
mollusca in the mantle, branchie, &c., differ from them in 
numerous horny and articulated limbs, and in a nervous sys- 
tem more nearly allied to that of the Articulata. ‘They will 
constitute our last class, or that of the CIRRHOPODA. 
FIRST CLASS OF MOLLUSCA. 
CEPHALOPODA. 
THEIR mantle unites under the body, forming a muscular 
sac, which envelopes all the viscera. In several its sides are 
extended into fleshy fins. The head projects from the open- 
ing of the sac ; it is rounded, furnished with two large eyes, 
and crowned with arms or feet, conical, fleshy, more, or less 
elongated, capable of being flexed in every direction, and ex- 
tremely vigorous, the surface of which is armed with suckers 
or cups, by means of which they adhere with great tenacity to 
every body they embrace. ‘These feet are their instruments of 
