ACTION OF LIMPETS ON CHALK. 



407 



with the concave side towards the animal, it reverses its action 

 and makes another curved line, in which each new groove is made 

 to the left of the last one. The first and second lines meet at a 

 more or less acute angle ; so the limpet moves over the ground 

 making curved lines in alternate directions, which form a zigzag. 

 Sometimes the angle which the curved lines make with one ano- 

 ther is so small, and the lines are consequently so close together, 

 that all, or nearly all, the surface of the chalk is subjected to the 

 grooving. In such cases patches of freshly abraded chalk more 

 than an inch square in area represent the work of a limpet pro- 

 bably in one tide. In other cases, when the animal had moved more 

 rapidly over the ground, the result of such an excursion appeared 

 in an open zigzag line. In these cases the length of the path of 

 the animal was sometimes more than 12 inches — the length of 

 the curved lines forming the zigzag being J of an inch, and the 

 width -^^ of an inch, but varying from that downwards, according 

 to the size of the animal by which they were made. 



On the part of the chalk foreshore immediately to the east of 

 Dover, which is generally free from great inequalities or debris, 

 limpets are very abundant, almost to the exclusion of other shell- 

 fish ; and down to near low-water mark there is little or no sea- 

 weed, excepting the young grow'th, which appears to be removed 

 with part of the surface on which it grows soon after it appears. 

 The number of limpets to a square foot varied, in the few cases 

 in which I had time to count them, from 5 to 9, omitting small 

 ones less than about half an inch. I'urther to the east along the 

 shore, where there has recently been a fall of the cliff, the shore 

 is encumbered with blocks of chalk. Many of these blocks were 

 covered with a matted coating of fine, semitransparent, ribbon- 

 like seaweed. The limpets had not yet obtained a footing here ; 

 but I found one or two, conspicuous by the little clearing they 

 had made in the midst of the seaweed. It was here possible to 

 ascertain the area of surface which one limpet could abrade and 

 keep clear of any but the youngest growth of seaweed. I mea- 

 sured some of these bare patches, and found them to vary from 8 

 to 14 square inches in area. The whole surface of these patches 

 was closely grooved, the less recent work being covered with an 

 incipient growth of seaweed. If one limpet could keep clear 14 

 square inches, it would require ten to keep clear a square foot, 

 which agrees with my former estimate (small ones being omitted) 

 of nine to a square foot where the rock was grooved all over. 



It is not easy to estimate the amount of chalk removed by 



LINN. JOURN. ZOOLOGY. YOL. XIV. 29 



