LITTOEINID^E. 339 



forms resulting from the substances on which they are fixed, 

 combined with the influencing effects of habitat, food, and 

 depth of water. 



I have recently examined and dissected 500 Anomia of 

 all forms, sizes and colours, from different habitats, and in 

 the endless variety of colour and markings of this proteiform 

 genus I have not discovered a specific character, either as 

 regards the anatomy or the external organs of this genus, that 

 would justify the creation of a single species. I have now done 

 with the Anomice, as the learned editors of the f British Mol- 

 lusca' have recorded these opinions in their interesting work, 

 though without any particular concurrence therein. But in 

 corroboration of these views I shall adduce some considera- 

 tions on another genus, which has largely contributed to the 

 increase of pseudo-species; I allude to that portion of the 

 genus Littorina designated L. littorea and L. rudis. 



This well-known family, as now constituted, consists of the 

 genera Littorina, Assiminia, Rissoa, and Truncatella. The 

 Lacunae of authors are scarcely distinguishable from the Litto- 

 rina littoralis', the animals are all but identical, and the two 

 genera appear to be separated on conchological grounds, the 

 groove in the columella, rather than on animal distinction. 

 I think it would conduce to the interests of science if the La- 

 cunce were merged in the genus Littorina, and marched pari 

 passu with Littorina littoralis as species. This view is adopted 

 below, where I shall show, malacologically, that the difference 

 between the animals of Lacuna and Littorina littoralis is 

 scarcely appreciable. The so-called Lacuna have only one or 

 two species instead of the eight or ten of authors. 



Assiminia was established by Dr. Gray, and differs chiefly 

 from the Rissoa ulvce and R. subumbilicata of Montagu in 

 having the eyes fixed at the extremities of the tentacula, in 

 consequence of being placed on adnate pedicles of concurrent 

 length. 



The Rissoce are very minute ; they inhabit the littoral and 

 laminarian zones ; the types of the first zone are the Rissoa 

 ulvaK and R. subumbilicata, and of the second, R. parva. 

 These are true littoral Rissoce. Many minute shells, which 



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