85 



Tarn. 2. MELANIADiE. 



Shell ovate, turreted ; mouth ovate; operculum free, 

 horny, ovate, spiral. The trunk of the animal is 

 more or less elongate, with 2 subulate tentacles, 

 with the eyes sessile on the outer sides of their base. 



This family contains only one rather anomalous 

 British fresh-water genus among its numerous marine 

 ones. There are several other fluviatile genera, as 

 Melania, Mekmopsis, and Potamides, which are now 

 only found in the warmer parts of the world, that were 

 once inhabitants of these regions, as they are found in 

 the fossil beds of the Isle of Wight, and the coast of 

 Hampshire. 



2. 1. Assiminia Leach MSS. (Assiminia.) 



Shell ovate, conical, solid; mouth ovate; tentacles 

 very short, scarcely larger than the tubercles on 

 which the eyes are placed, and united to their side, 

 (p. 78. f. 4, 5, 6.) 



The animal differs from JLittorina in the ap- 

 parent position of the eyes, which is an anomaly 

 among the water or Ptenobranchous Mollusca. 



This animal was first indicated, and its peculiarites 

 pointed out, in my paper above quoted, in 1821 ^ 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 appearing to be placed 

 at the end of the tentacle ; but I believe that they are 



