352 LITTOEINID.E. 



exclusively confined to that genus, and which must, I think, 

 fix the Lacunas of authors for ever as one of its sections. 



With regard to the aid derived from the tongues of the 

 Gasteropoda for generic or specific distinction, I am inclined 

 to think its importance overrated, because no two species of 

 the same genus have a precisely similar disposition of the 

 rachis, uncini, and arrangement of the spines and inter- 

 weavings of the lingual riband. This fact sets at rest generic 

 views ; the tongues, at best, are of mere specific value. I 

 have examined hundreds, and can make nothing of them that 

 can at all be depended on, from their extremely variable struc- 

 tures. The tongues of great numbers of the minor species 

 cannot without extreme difficulty be obtained by the scalpel ; 

 they can only be detected after maceration, and compression 

 under a powerful microscope, and the comparison of these 

 minute species is attended with difficulties and very unsa- 

 tisfactory results. The oothcca of the Mollusca may be useful 

 in comparison, if they can be obtained, and identified to be- 

 long to certain species. 



I conclude, and insist on the foregoing positions, with as 

 much tenacity as courtesy will allow to the phrase. I cannot 

 even consent that the Lacunas be considered a subgenus of 

 the LittorincB. I think the term subgenus an unsatisfactory 

 and hybrid expedient to attempt to express an intermediate 

 state that does not exist; with me, subgenera are resolved 

 either into distinct species or genera. If I might consider 

 that those who use the term subgenus mean to define it as an 

 aggregation of particular or aberrant species of a distinct 

 genus, I would accept the definition, but not the term, which 

 ought to be section, as that of subgenus seems to imply 

 something beyond divisional arrangement. 



The Littorina puteolus with us, and its congener L. vincta, 

 though examined, are not described. The Littorina crassior 

 we have not seen. 



LITTORINA PUTEOLUS, nobis. 



Lacuna puteolus, Turton. 



,Brit. Moll. iii. p. 58, pi. T>. f. 7, 8, .9 ; pi. 7-1. f. 9. 



