EXPLANATION OF THE FIGURES. 207 



f g, the arms, or tentacula. 



//, two of the arms longer than the rest, and often called 



tentacula, or pedicellate arms. 

 g g, the eight ordinary arms, covered internally with little 



acetabula, or cups. 

 Fig. 2. Cymbulia Peronii. 

 a, the shell. 

 h b, the fins, attached to the sides of the head and neck. 



c, the head. 



Fig. 3. LlMN^US STAGNALIS. 



a, the spiral shell. 



b, the supraoral flap, or veil, 

 c c, the tentacula. 



d, the eyes. 



e, the head. 



Fig. 4. FUSUS CORNEUS. 



a a, the shell. 



b, the head. 



c c, the tentacula. 



d d, the eyes. 



e, the proboscis. 



/, the respiratory process, or siphon. 



g g, the foot. 



h, the operculum. 

 Fig. 5. Mya truncata. 



o, the shell. 



b, the siphon-tube. 

 Fig. 6. Terebratula, showing the two arms. 



Fig. 7. ASCIDIA INTESTINALIS. 



a, the cartilaginous sac. 



b, the upper orifice, for water. 



c, the lower orifice, for excrement. 

 Plate XXI. fig. 8. Animal of a Turbo. 



a a, the foot. 



b, the operculum. 



c, the proboscis. 



d d, the tentacula. 



e, the eyes, at the base of the tentacula externally, 



82 



