MOLLUSCA, 133 



sions. They have their origin on the ventral side of the 

 mouth, between that organ and the funnel. The suckers 

 are pedunculated, with their margin strengthened by a corn- 

 eous ring, furnished with teeth. The sac is furnished with 

 fin-like expansions, and strengthened internally by corneous 

 or testaceous ribs or plates. The head is divided from the 

 sac on all sides by a neck. The margin of the anus is sur- 

 rounded with tentacula. 



GENUS SEPIA. The sac is furnished on each side through- 

 out its whole length with a narrow fin. 



The suckers are irregularly scattered on the arms and 

 feet. The back is strengthened by a complicated calca- 

 reous plate, lodged in a peculiar cavity. This plate has 

 been long known in the shop of the apothecary under the 

 name Cuttle-fish bone, which was formerly much prized in 

 medicine as an absorbent, but is now chiefly sought after 

 for the purpose of polishing the softer metals. It is some- 

 what ovate, flatly convex on both sides, and thickest where 

 broadest. The superior half, or the one next the head, is 

 the longest, rounded at the extremity, and thin. The in- 

 ferior portion becomes suddenly narrow, and ends in a point. 

 It may be considered as consisting of a dermal plate, con- 

 cave on the central aspect, having u its concavity filled up 

 with layers which are convex on their central aspect. 



According to our observations, the dermal plate appears 

 to consist of three different laminae, arranged parallel to one 

 another. The external or dorsal layer is rough on the sur- 

 face, and marked by obscure, concentric arches towards 

 the summit, formed by minute knobs, which become larger 

 towards the base, where they appear in the form of inter- 

 rupted transverse ridges. It is uniform in its structure, and 

 the tubercles possess a polish and hardness equal to porcel- 



