862 



MR. E. S. RUSSELL ENVIRONMENTAL 



[Nov. 26, 



Size of High- water Limpets.— Jt seems to be the opinion of 

 most authorities that high- water limpets are on the whole smaller 

 than low- water limpets. 



Canon Norman (12) says definitely: — "It will be found to be 

 a general rule with regard to the Limpet, that the nearer high- 

 water mark the shells are taken, the higher spired, more strongly 

 ribbed, and smaller it will be ; and that the lower down it lives, 

 the flatter, less ribbed, and larger it becomes." While my obser- 

 vations entirely corroborate the truth of the statement that high- 

 water limpets are typically high-spired, yet I find, foi- one area 

 at least, that the proportion of large shells is greater at high- 

 water than at low- water. Table III. shows that of 300 high- water 

 limpets collected without conscious preference of large over 

 small, 161, or 53| per cent., were under 40 mm. in length, and 

 139, or 46 J per cent., were over 40 mm. From Table IV. it 

 appears that 234, or 78 per cent., of the low-water shells were 

 below 40 mm., and only 66 or 22 per cent, were above 40 mm. in 

 length. The average maximal size of the high-water shells is 

 about 55 mm., of the low- water shells about 50 mm. For the 

 locality therefore in which these limpets were collected, the 

 proportion of large limpets was considerably greater at high- 

 water than at low- water. 



Of course that does not mean that here and there a low- water 

 limpet may not be found as large as, or larger than, any high- 

 water limpet. As a matter of fact, of the six specimens over 

 60 mm. long which I obtained among the 1000 collected, three 

 came from high-water, and three from low- water level ; and the 

 largest of these, a limpet 66 mm. long, came from low-water level. 



III. Sheltered and Exposed Limjyets. 



Table V. gives the mean ratios of 100 limpets collected from 

 sheltered situations in one definite locality, and of 100 limpets 

 collected from exposed situations in the same locality. 



Table V. 

 Sheltered, 



Exposed. 



