ASSIMINIA. 21 



sessile, on the outer side of the base of the ten- 

 tacles; jaws horny; teeth in 7 longitudinal series, 

 converging. Mantle-edge simple. Gill single, 

 formed of very numerous flat free cross-folds, 

 occupying nearly the whole of the inner sur- 

 face of the cavity. Foot moderately broad for 

 walking. Opercular lobe simple. Operculum 

 spiral, horny, of gradually enlarging whorls. 

 Amphibious ; marine, or in brackish water. 



1. AssiMiNiA Leach MS. (Asslminia.) 



Shell ovate, conical, solid ; mouth ovate ; tentacles 

 simple, very short, scarcely longer than the tu- 

 bercles on which the eyes are placed, and united 

 to their side ; operculum horny, ovate, of a few 

 rapidly enlarging whorls, (p. 23. f. 3.) 



The animal differs from Littorina in the apparent 

 position of the eyes, which is an anomaly among the 

 water or Ptenobranchous Mollusca. 



This animal was first indicated, and its peculiari- 

 ties pointed out, in my paper above quoted, iaH21 

 when I made the following remarks on its structure. 

 " The animal of this shell differs from all others of 

 the order (to which it belongs), by the eyes appear- 

 ing to be placed at the end of the tentacle ; but I 

 believe that they are placed on a peduncle as long 

 as the tentacle, and the peduncles and tentacula are 

 soldered together." 



Mr. Berkeley, in his description of tlie animal 

 (^Zool. Journ. v. 429.), observes, — " The most re- 

 markable circumstance in this animal is the position 

 c 3 



