OF SOME COMMON MARINE ANIMALS. 



255 



with Balanus on the rocks (fig. 7), the most abundant shell-fish are Patella 

 vulgata, Purpura lapillus, and several species of Littorina. Ten counts of 

 Patella gave an average of 29 to the square foot, the highest record being 37. 

 Two counts on square feet where Purpura seemed numerous on the limestone 

 rocks at Port St. Mary gave 72 and 101 respectively. The method adopted 

 in all these cases was to plant a wooden frame measuring one square foot 

 internally down on the rock and count or remove all that lay inside it. 



In half-a-dozen small shallow rock-pools on the limestone at Port St. Mary 

 the common red anemones (Actinia equina) gave respectively 30, -17. GO, 49, 

 55, 37 to the square foot, taking the pools in order from the highest down- 

 wards towards low water. The average is over 40, and the range (30 to 60) 



Fig. 7. — Rock surface al Port Erin covered with Balanus, Patella, &c. 



is not great — suggesting that such little pools having a surface of about two 

 square feet and a depth of a few inches, and generally lined by Nullipores 

 and Corallina, can only support some 40 or 50 anemones each. 



On the sand at Port Erin the most conspicuous marks are the '"casts*' of 

 the burrowing worm Arenicola marina (the fisherman's " Lug-worm "'), and 

 from our counts we find 11,800 worms in a rectangle measuring 100 yards 

 by 30 yards at low tide — that is about four to the square yard : while a little 

 further up the shore, in a square of 10 yards each way, we found G53, or 

 u'5 worms to the square yard — and this, moreover, on an area where both the 

 fishermen and the visitors were constantly digging the worms for bait. 

 Very much larger numbers than these — up to 30 or 40 to the square yard — 

 have been counted on some beaches, and Ashworth has estimated that at 

 Musselburgh, in a zone at low tide about a mile in length, there are from 

 3 tj 4 million worms*. 



* L. M. B. (_'. Al'inoir xi, Arenicola ; 



904. 



