ELEMENTS 



CONCHOLOGY. 



Order 3. PLEUROBRANCHIATA. 



Branchiae ; placed on the right side of the animal, either beneath 

 the edge of the mantle or in a special cavity. 



In the Order of Pleurobranchiata, or right-gilled Gastropods, the shell 

 is more subordinate in value to the soft parts than iu either of the preced- 

 ing orders. It includes a number of complicated, curiously formed, and 

 brilliantly coloured, but, alas ! horribly smelling, mollusks, which have no 

 shell whatever ; some have only a rudimentary or membranaceous shell, and 

 in none is the shell absolutely external or of solid structure. The families 

 are : — 



BULLACEA. APLYSIANA. SeMIPIIYLLIDIANA. 



Family 1. BULLACEA. 



Genus 1. BULLA, Klein. 



Animal; head generally broad and truncated, with the eyes indis- 

 tinct or loanting ; disc large and bulky, furnished with ample 

 lobes which serve as swimming -organs, and are used for more 

 or less investing the shell ; tentacles sometimes modified into an 

 anterior reflected lobe, mostly furnished with a gizzard. 



Shell ; horny or shelly, lightly convoluted, more or less enveloped 

 by the animal. 



Bulla shells, of which as many as a hundred and fifty species are known, 

 from different parts of the world, are of light inflatcdly-convoluted growth, 



VOL. II. u 



