238 Natural History of Molluscous Animals 



H^ale, copied from Rang. Cuviera, copied from Rang. 



beyond the shell when the animal is in motion, but at other 

 times retracted, and fixed upon a common stalk by a point a 

 little removed from one of the ends.* 



The Gasteropoda which arrange themselves under this 

 division form a very natural and interesting order, appro- 

 priately named by Cuvier the Nudibranchioe. These are 

 naked snail-like Mollusca which live only in the sea; and 

 they would scarcely attract our notice amid the myriads of 

 curious creatures that are around them, were it not for the 

 ornament and singularity of their branchial appendages. 

 Their position is always on some part of the back, either 

 ranged in one or more series along its margins, as in Glaucus, 

 Eohdia, and the Tritomadce, or clustered on a point of the 

 medial line near the hinder extremity, as in the Doris and its 

 allies, which have the power of concealing them within the 

 body when danger threatens from without. In shape they 

 vary more than in position : they are simple filaments in 

 Eolidia ; in Glaucus they are fan-shaped fins ; in Melibae\z 

 clubbed processes, covered with little hispid tubercles, or, as 

 in Scyllea, with little tufted bouquets of very delicate fila- 

 ments ; and in the r Yx'\X,omadce and Doris they assume a more 

 or less perfectly plumose or arborescent appearance. 



There are other Gasteropoda in which, although not so 

 fully exposed as in the preceding order, the gills are still only 

 slightly concealed by some lap or fold of the cloak. The 

 genera Patella*, as now restricted, and Chiton afford ex- 

 amples where the branchiae, in form of a cord composed of 

 pyramidal processes, or of close-set and parallel transverse 



* Rang's Manuel de VHistoire Naturelle des Mollusques, p. 38. tab. 2. 

 fig. 4?. An excellent work, which I regret I had not the assistance of in 

 the compilation of the preceding letters. 



f Blainville, however, maintains that Patella is pulmoniferous. (Manuel, 

 p. 125.) 



