360 Mr. W. Clark on the Littorinidae. 



Littorina, Ferussac. 



Littorina neritoides, Linnaeus. 

 Turbo petrceus, Montagu et aliorum. 



Animal spiral ; mantle even with the shell ; the head is a long 

 proboscidiform cloven muzzle, the upper part of an intense black 

 cloud-colour ; orifice of the mouth white with a vertical fissure ; 

 tentacula awl-shaped, moderately long, flattened ; eyes large, not 

 on pedicles, but placed on the substance of the skin at the bases 

 of the tentacula, inclining externally only in a trifling degree. 

 The buccal mass is plain brown, supported by two thin coriaceous 

 plates of the same colour, from whence a very long white spiny 

 tongue proceeds to the stomach, and there lies coiled as in Lit- 

 torina littorea ; but it is proportionately longer than in that spe- 

 cies, being 2 inches long. Foot nearly as in L. littorea, very 

 slightly auricled and curved in front, rounded posteriorly to a 

 terminus, which is a little jagged or dentated, forming an oval 

 when not in action, but on the march a very elongated oval ; 

 above its colour is black ; underneath a pale lead ground mixed 

 with two shades of white and one of purple. These colours are 

 divided into three portions j the anterior one is the narrowest, of 

 an intense hyaline white, the middle is also hyaline, and the third 

 is hyaline pale purple. The foot is not strictly divided into two 

 longitudinal half-parts as in L. littorea, but at the anterior part, 

 where the intense hyaline white terminates, appears transversely 

 broken or furrowed, so as to allow of a subdued alternate undu- 

 latory gait, or quality of progression, something like that of L. 

 littorea, in which the whole of the longitudinal half is first ad- 

 vanced, and then the other ; but here only half of the anterior 

 part of the foot 13 moved forward, and then the other, and so on, 

 dragging the other part in alternate times. 



This alternate action of parts of the foot is a very singular 

 character, which obtains, more or less, in all the true Littorina, 

 and is with very few exceptions confined to that genus. There is 

 only one branchial plume, and the internal and external organs 

 are nearly those of L. littorea. The sexes are distinct in all the 

 Pectinibranchiata. I ought to have mentioned the suboval cor- 

 neous dark operculum, pointed superiorly with about two rapidly 

 increasing gyrations, the nucleus being at the basal end. 



This species is one of those that inhabit the highest levels of 

 the littoral zone, and often dwells for an indefinite time far be- 

 yond even the spray of the sea. It appears a mystery how the 

 branchiae are kept moist ; I suspect the minute saline particles 

 carried by the winds suffice, especially as the long exposure to 

 atmospheric influences has almost rendered the branchiae of pul- 

 nioniferous quality. They clothe the rocks in myriads on the 



