GASTEROPODA. 



279 



Fig. 120. Patella 



vulgata. 

 (Original, Wiltoa.) 



Example, P. longicostata. PL XI., Fig. 22. 



Shell oval, with a sub-central apex; surface smooth, or 

 ornamented -with radiating strice or ribs; 

 margin even or spiny ; interior smooth.. 



Animal with a continuous series of bran- 

 chial lamellse ; mantle-margin fringed ; eyes 

 sessile, externally, on the swollen bases of 

 the tentacles ; mouth notched below. Lingual 

 teeth 6, of which 4 are central, and 2 lateral; 

 uncini 3. Pig. 120 shows the teeth, but not 

 the uncini of P. vulgata. The Caj^e limpets 

 (e.g. P. denticulata) have a minute central 

 tooth, which is wanting in any other species 

 hitherto examined. (Wilton.) 



The dental canal of the common British 

 limpet (P. vulgata) is rather longer than its shell; it lias 160 

 rows of teeth, with 12 teeth in each row, or 1,920 in all. 

 (Forbes.) The limpets live on rocky coasts, between tide- 

 marks, and are consequently left dry twice every day ; they 

 adhere very firmly by atmospheric pressure (15 lbs. per square 

 inch), and the difficulty of detaching them is increased by the 

 form of the shell. On soft calcareous rocks, like the chalk of 

 the coast of Thanet, they live in pits half an inch deej), pro- 

 bably formed by the carbonic acid disengaged in respiration ; on 

 hard limestones only the aged specimens are found to have worn 

 the rock beneath, and the margin of their shell is often accom- 

 modated to the inequalities of the surrounding surface. These 

 circumstances would seem to imply that the limpets are 

 sedentary, and live on the sea-weed within reach of their 

 tongues, or else that they return to the same spot to roost. On 

 the coast of Northumberland we have seen them sheltering 

 themselves in the crevices of rocks, whose broad surfaces, over- 

 grown with nullipores, were covered with irregular tracks, 

 apparently rasped by the limpets in their between tides 

 excursions.* 



The limpet is mucn used by fishermen for bait ; on the coast 

 of Berwickshire nearly 12,000,000 have been collected yearly, 

 until their numbers are so decreased that collecting them has 

 become tedious. (Dr. Johnston.) In the north of Ireland 

 they are used for human food, especially in seasons of scarcity ; 



» If limpets are placed in stale water, or little pools exposed to the hot sun, they 

 creep out more quickly than one would expect; the tracks they leave are very 

 peculiar, and not likely to be mistaken when once seen. 



