350 LITTORINID^. 



canal of the sac that contains the viscous fluid. The neck of 

 the animal is simple and free from membranous lappets, as is 

 the case in all the Littorinfe. The fsecal pellets are elongated, 

 slender, subcylindrical, having the apices tipped with a dark 

 hue. The verge is a long, simple, arcuated, flattish, pale 

 yellow process, regularly tapering from its insertion under 

 the right tentaculum to a fine point. The operculum is pale 

 horn-colour, subelliptic; nucleus excentric, sublateral, abut- 

 ting on the columella, with 2^ volutions, the last of which 

 rapidly unites with the margin. We repeat the remark on 

 the internal organs of the Littorina littoratis, in comparison 

 with this species, that they are identical. 



Malacologists will observe, that in the two species the 

 internal and external organs are essentially the same; the 

 only variations are, that in Littorina pallidula, the caudal 

 filaments, the expansions of the operculigerous lobe, and the 

 form of the organe aenerateur, are not precisely similar to the 

 parts in L. littoralis. The former are very variable specialties 

 and cannot be depended on : ex. gr. the Lacuna puteolus of 

 authors is without caudal processes, or at least they are obso- 

 lete ; the same observation may be made of the Rissoae, no 

 two animals of the same species being similar in respect of 

 caudal accessories, and many are without them. The male 

 organs of the two undoubtedly vary in structure ; the groove 

 or lacuna in the pillar, from whence the generic title, is a 

 mere modification of the umbilicus, which, from its variable- 

 ness, is not of specific value, and is quite misapplied to generic 

 determination. All the variations we have mentioned arc 

 specialties of slight consideration, which cannot be put in 

 competition with the essential generic characters of the foot, 

 and its singular plan of locomotion, which stamp the so- 

 called Lacunae of authors as genuine members of the genus 

 Littorina. 



Since the above was written, I have reviewed, in a living 

 state, all the Lacunae of authors, except the " crassior," and I 

 think I am authorized to be still more " tenax propositi/' that 

 they are a section of the genus Littorina, and cannot be 

 severed from it without violence to true generic value. I find 



