21 



ovate ; tentacles very short, scarcely longer than the tubercles on 

 which the eyes are placed, and united to their side, p. 78, f. 4, 5, 6, 

 observing, "the animal differs from Littorina in the apparent posi- 

 tion of the eyes, which is an anomaly among the water and Cteno- 

 branchous MoUusca ;" and after quoting Mr. Berkeley's deseription 

 of the tentacula I observe, — " I am indined to retain my former 

 theory, for if the pedicel of the eye of this genus is minutely exa- 

 miued, it will appear to be formed of two parts united by a suture." 



In 1852, having obtained permission of the family, I printed 

 Dr. Leach's ' Molluscorum Britannise Synopsis ' above referred to, 

 and he there described the genus — "Assiminia. Testą conica, 

 spira mediocris. Animal tentaculis duobus breribus, apice paulo 

 angustioribus obtusis, ad apicem ocuUgeris, instructum ; ocuU parvi, 

 rotundi ; operculum tenue." 



"From the form of the shell this genus might be considered as 

 belouging to the second stirps {testą conica, spira brevis), but the 

 animal proves that it is more nearly allied to Sabancea than to any 

 other of the British genera." (p, 155. t. 9. f. 4, 5.) 



Lately some doubt has been attempted to be thrown on the 

 distmctness of the genus, which it has been proposed should be 

 united to the genus Truncatella of Risso. 



Considering the very great similarity which often exists in the 

 general appearance of the animals of very distinct genera of MoUusca, 

 — a similarity so great, that if a person was to place before me, without 

 the shell or operculum, the animal of the genera Murex, Triton, Pur- 

 pura, Fasciolaria, Columbella, &c., I should not be able to distinguish 

 one from the other without the examination of the teeth or the lin- 

 gual membrane, and that would only enable me to separate Triton, 

 Cassis and Fasciolaria from each other and from Murex, Purpura a.nd 

 Columbella, and not the three latter genera from each other; and it is 

 the šame with the animals of several other orders and families ; — 



Fig. 1. 



Kg. 2. 



1 . Truncatella truncatula /3. 



a. With foot extended, in the act of 



drawing up the shell. 



b. Side view. 



c. Seen beneath as crawling up a 



glass, when the muzzle is ex- 

 serted. 



2. Assiminia Grayana. 



Uuder side of animal and shell. 



Side view. 



Front of foot, shovving how the 

 lower lamina of tlie foot pro- 

 jects beyond the upper. 



yet the animals of the two genera Assiminia and Truncatella (see 

 figs. 1 and 2) proposed to be united, are so uulike in general ap- 



