EXPLANATION OF THE PLATES*. 



PLATE I. 



Nautilus Pompilius, in the prone positionf, with its natural relation to the shell 

 shown by a section of that part in outUne. 

 a. a. The mantle. 



b. Its dorsal fold, applied to the involute convexity of the shell. 



c. Its free anterior margin. 



d. The orifice for the passage of the funnel. 



e. The convexity produced by the ovarian gland. 



/./. Tlie horny girdle for the adhesion of the mantle to the shell. 

 g. Tlie horny laminae covering the extremity of the left shell-muscle. 

 h. A portion of the shell, which was left adhering to this muscle. 

 i. i. i. The membranous tube or siphon which traverses the testaceous tubes 

 in the camerated portion of the sheU. 

 k. The funnel. 



I. The left lateral process of the funnel, 

 m. The left cms or piUar of the funnel. 



n. Tlie hood, or ligamento-muscular disk that surmounts the head. 

 0.0. The exterior digitations of the left side. 



0. The larger one, with a papillose surface like that of the hood. 

 p. p. The digital tentacles, protruded from their sheaths. 



q. The groove which separates the hood from the papillose digitation. 

 r. r. The ophthalmic tentacles. 

 s. The eye. 

 t. Its peduncle. 



u. The inferior ridge, or rudimentary eye-lid. 

 V. The ridge running from this to 



* All the parts are represented of the natural size, except where it is otherwise expressed, 

 t In using the terms relating to aspect and situation in the preceding description, this is considered 

 as the natural position of the animal. 



