PUPA. 161 



and Cypraa among marine ones, it only forms the 

 complete mouth to its shell once in its life. (See 

 Phil Trans. 1833.) 



These shells are called Pupa, Puppet, or Doll, 

 because they resemble children in their swaddling- 

 clothes. 



a. Peristome margined, reflexed; the young shell with 

 a transverse series of short triangular plates. 

 (Lauria Gray.) 



Mr. Alder has observed that Pupa umbilicata and 

 P. anglica have a very curious and elaborate internal 

 structure. They have a raised thread-like lamina, 

 running spirally round the columella in the manner 

 of a corkscrew, and another similar lamina running 

 spirally in the centre of the upper side of the whorls; 

 and there are set at short distances small flat testa- 

 ceous plates similar in situation to the septa in Nau- 

 tilus lacustris. This complicated structure is, no 

 doubt, intended to answer some useful purpose in 

 the economy of the animal ; but what is its use be- 

 sides the protection of the animal in a young state, 

 he has not been able to discover. It is not continued 

 through the lower whorls, and is most distinctly seen 

 in the young shells. This structure is not found in 

 the young of Pupa marginata, P. edentula, and P. 

 sexdentata. 



70. 1. PUPA cylindracea. Umbilicated Chrysalis 

 Shell. Shell cylindrical, bald, smooth, brown- 

 ish ; whorls five to seven ; mouth elongate 

 lunate, with a single laminar tooth united to 



