PTEROCERA. 109 



claws, which are conjectured to serve as anchors in time 

 of need. 



The Bostellaria, limited in species, and principally affect- 

 ing China and the Molucca Islands, forms an elegant 

 fusiform shell. The disc is divided into two separate por- 

 tions, and the animal is thus enabled to change his place 

 of abode by a succession of leaps, instead of the usual 

 method of contraction and dilation. 



In like manner, also, the occupant of the Pterocera 

 progresses by means of a very restricted kind of leap. Tor 

 this purpose the disc is curiously two-forked, and in the 

 stouter branch, which is commonly pedunculated, appears 

 an eye of unusually large proportions. This eye is ap- 

 parently more fully developed than in any others of the 

 Gastropods ; it covers the summit of the stout, truncated, 

 and tentacular branch already mentioned, and is composed 

 of a transparent horny material containing an iris, which 

 differs in colour according to the species, and is wonderfully 

 constructed for the transmission of light into an inner 

 chamber. 



Equally curious is the faculty possessed by the mantle 

 of expanding into several finger-like divisions when about 

 to suspend its masonic labours, each secreting a massive 



