GASTEROPODA. 



279 



or 



Fig. 120, Patella 



vu gata. 

 (Original, Wiltoa.) 



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



Shell oval, -u-itti a sub-central apex ; surface smootli, 

 ornamented -with radiating strice or ribs; 

 margin even or spiny ; interior smooth. 



Aniimd ^ih.n. continuous series of bran- 

 chial lamellao ; 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 Cape limpetg 

 (e.g. P. denticulata) hare 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 has 160 

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

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

 marks, and are consequently left dry twice eyery 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 deep, pro- 

 bably formed by the carbonic acid disengaged in respiration ; on 

 hard limestones only the a,ged 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 woiiM expect; the tracks they leave ai'e very 

 peculiar, and not linely to be mistaken when ouce seen. 



