LAMARCK. 535 



Order V. Heteropodes. No arms in coronet on the head ; 

 no foot under the belly or throat to creep upon. 

 One or several fins, not paired nor regular in their 

 I^osition. 



Order I. PTEROPODES. 



There is no subdivision of this order w^hich contains the 

 genera Hyalaca, Clio, Cleodora, Limacina, CynibuKa, and 

 Pneuniodermon. 



Order II. GASTEROPODES. 



_ I. Section. Branchias, whatever their position, raised 

 either in filaments, or lamina?, or combs or tufts. They 

 breathe water only. {Hydrohranches.) 



(a) Branchiae external, placed above the mantle, either 

 on the back or on the sides, and never in a special cavity. 

 Les Tritoniens. 

 (6) Branchiae external, placed under the margin of the 

 mantle ; and disposed in a longitudinal series either 

 around the body or on one side only, but not in a special 

 cavity. 



Les Phyllidiens. 

 Les Semi-Phyllidiens. 

 (c) Branchiae placed in a special cavity on the back, 

 situated forwards near the neck. 



Les Calyptraciens. 

 {(l) Branchiae placed in a special cavity towards the ^jos- 

 terior part of the back, and covered either by the 

 mantle or by an opercular shield. 



•f- No tentacula. Les Bulleens, 



f -f With tentacula. Les Laplysiens. 



II. Section. Branchije creeping, under the form of a vas- 

 cular network, on the walls of a special cavity, the aperture 

 of which the animal opens and shuts at pleasure. They 

 breathe the atmosphere only. {Pneumobranches.) 

 Les Limaciens. 



Order IIL TRACHELIPODES. 



I, Section. T. without a prominent siphon, and in general 

 breathing by a hole. The most part of them are herbivo- 

 rous and furnished with jaws. Shell with the aperture 

 entire, having at its base neither a dorsally directed emaro-i- 

 nation nor canal. (Les Ph[itlpliages.) 



* Trachelipods breathing the air. Shell spiral, even, 

 not distinctly nacred. 



