186 MALACOZOA. GASTEROPODA. TEGTIBRANCHIATA, 



ORDER VI. GASTEROPODA INFEROBRANCHIATA, 



The Infero-branchiate Gasteropoda, having the respi- 

 ratory organs in the form of lamellae beneath the pro- 

 jecting edge of the mantle, the body always naked and 

 more or less tubercular, have no representatives in our 

 seas. 



ORDER VII. GASTEROPODA TECTIBRANCHIATA, 



Respiratory organs composed of branched or pectinated 

 laminae, attached along the right side or on the back, 

 and more or less covered by the mantle, which generally 

 contains in its substance a thin shell. 



They are all marine, and have a very complex digestive 

 apparatus. 



FAMILI I. BULL^EINA. 



Animal with the body subglobose, oval, or oblong, 

 divided into two parts, of which the anterior is often 

 furnished with lateral lobes ; head destitute of tentacula, 

 or having these organs rudimentary or united to form an 

 anterior tentacular disk ; the branchiae placed on the 

 back, protected by the mantle, often also by a shell. 



Shell none, or if present external or internal, generally 

 very thin and convolute. 



GENUS 1. BULL.EA. 



Body oval, elongated, somewhat convex above, trans- 

 versely divided into two parts ; lateral lobes of the foot 

 with a thickish margin, and bent upwards ; head scarcely 

 distinct, without tentacula ; branchiae dorsal, placed 

 under the posterior part of the mantle. 



Shell concealed in the substance of the mantle, over 

 the branchiae, very thin, partially bent in a spiral form, 

 without spire or columella, the aperture very wide. 



