Mr. W. Clark on the Littorinidse. 361 



South Devon coasts. I sum up, and conclude the present species 

 to be a true LUtorina. 



I omit a description of the animal of the very common L. lit- 

 toralis, which I reserve as a standard of comparison for my me- 

 moir on the animals of the Lacunae. 



Littorina littorea, auctorum. 



This exceedingly common, but very curious and interesting 

 animal, has not met with the attention it deserves ; we are sure 

 that we shall afford gratification in producing a detailed account 

 of it. 



Animal spiral ; mantle simple, exactly lining the aperture of 

 the shell ; the head is long, cylindrical, not deeply cloven ; mouth 

 a vertical fissure, and with the neck and tentacula are marked on 

 their upper surfaces on a yellow ground, with very close-set dark 

 transverse lines, which, with the lead-colour anastomosing lon- 

 gitudinal waved markings, give the animal almost a black ap- 

 pearance. The tentacula are moderately long, conical, pointed, 

 very tumid at their bases, black above, white beneath, on which, 

 a little raised, the eyes are set externally. The foot is a very 

 singular organ, short, rounded before and behind, scarcely 

 auricled, and when in action forms an oblong suboval disk, 

 divided by a central sunken line into two longitudinal lobes, 

 which, when the animal marches, are each advanced alter- 

 nately with an undulating vermicular motion. This curious lon- 

 gitudinally divided foot and peculiar locomotion are only to be 

 found in one or two other genera ; they are particularly conspi- 

 cuous in the Phasianella pullus. The under part of the foot is 

 yellowish white, bordered by a deep line at a little distance 

 within the margin, from which fine transverse ones radiate, 

 giving the foot the appearance of being encompassed by a fine 

 fringe ; the upper posterior part carries a dark, corneous, suboval 

 operculum, with about two turns of elliptical striae, and a very 

 excentric nucleus. The buccal apparatus is a deep red fleshy 

 mass, supported by two thin coriaceous plates, between which, in 

 ordinary-sized animals, a long, at least two inches, riband-like 

 white spiny tongue issues, passing down the oesophagus, and be- 

 comes closely coiled in the stomach; its termination is tinged 

 with red ; immediately behind the buccal mass is the oesophageal 

 cordon, which consists of only two white subrotund flattish gan- 

 glions, one on each side, and behind them are the salivary glands, 

 each formed of a mass of foliaceous granules ; there is only one 

 branchial plume, of light yellow, attached to the left side of the 

 mantle and neck of the animal ; the verge is a Jarge flat or- 

 gan grooved longitudinally, ridged transversely, dentated on one 

 side with two points, one below the other, the lower one with 



