FAMILY 1. BULLACEA. 47 
Family 1. BULLACEA. 
Testa fragilis, leviter convoluta, patentissima, partim vel omnino interna. 
The family of the Bullacea, ‘‘ Les Bulléens”’ of Lamarck, ‘‘ Les Acéres”’ of 
Cuvier and De Férussac, include a small group of mollusks provided with 
a fragile, lightly-convoluted shell, either partially or altogether concealed 
within the mantle. They have no great affinity with the Macrostomata 
or the Tubispiracea, but are closely allied to the Semiphyllidiana ; for to 
whatever part of the system they have been assigned by authors, they are 
always to be found associated with the Aplysie and Dolabelle, from which 
they differ only in having no tentacula. 
Those of the Bullacea that are conchiferous may be included in the 
following genus : 
Butta. 
BULLA, Klein. 
Testa tenuis, interdum fragilissima, ovata vel subcylindrica, laevigata, 
leviter convoluta ; spira brevi aut depressa, aut concava, rard pro- 
minente ; apertura magna, interdum patentissima, labio versus api- 
cem paululum inflexo. 
The Bulle appear to have excited no little confusion amongst the early 
naturalists ; for whilst they were described by Muller under the title of 
Lobaria, their shells were figured by Klein and others under that which 
is now retained ; and both these were introduced by Gmelin in his edition 
of the ‘Systema Nature’ as animals of a different order ; the title of Lo- 
baria is, however, still retained by De Blainville in reference to some 
naked mollusks belonging to this family. The genus Bulla of Linnzus 
