PUPA. 
161 
and CyprcBCB 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^ rejlexed; the young shell with 
a transverse series of short triangular plates. 
(Lauria Gray.^ 
Mr. Alder has observed that Pupa umhilicata 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 
M 
