HELICIDJE. 193 



front, and the animal does not form the reflexed lip 

 until it has arrived at maturity ; consequently, like the 

 ClausilicB among land shells, and the Strombi and Cy- 

 prcBCB 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. 



* LAURIA Gray. 



Peristome margined, reflexed ; the young shell with a 

 transverse series of short triangular plates. 



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 besides 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. 



65. 1. PUPA umbilicata. Umbilicated Chrysalis 

 Shell, (t. 7. f. 78.) Shell cylindrical, bald, 

 smooth, brownish ; whorls five to seven ; mouth 

 elongate lunate, with a single laminar tooth 



