154 MANUAL OF THE MOLLUSCA. 



Forbes has very happily suggested that the cyclo-brancliiate gill of patella is, 

 in reality, a single, long branchial plume, originating on the left side of the 

 ueck, coiled backwards round the foot, and attached throughout its length. 

 This view is coniirmed by the circumstance that the gill of the sea-weed 

 limpets {nacellce) does not form a complete circle, but ends without passing 

 in fi'ont of the animal's head. 



Patella, L. Kock limpet. 



Etym., patella, a dish. Si/n., helcion, Moutf. 



Ex., P. longicostata, PL XI., fig. 22. 



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

 radiating strise or ribs ; margin even or spiny ; interior smooth. 



Animal with a continuous series of branchial lamellae ; mantle -margin 

 fi'inged ; eyes sessile, externally, on the swollen, bases of the tentacles ; mouth | 

 notched below. Lingual teeth 6, of which 4 are central, and 2 lateral ; i 

 uncini 3. 



The tongue of the common British limpet (P. \Tdgata) is rather longer j 

 than its shell ; it has 160 rows of teeth, mth 12 teeth in each row, or 1,920 I 

 in all (Forbes.) The limpets live on rocky coasts, between tide-marks, and | 

 are consequently left dry twice every day ; they adhere very lii'mly, by at- j 

 niospheric pressure (151bs per square inch), and the difficulty of detaching j 

 them is increased by the form of the sheU. On soft calcarious rocks, Like the j 

 chalk of the coast of Thanet, they live in pits haK an inch deep, probably \ 

 formed by the carbonic acid disengaged in respiration ; on hai-d limestones ; 

 oidy the aged specimens are found to have worn the rock beneath, and the \ 

 margin of their shell is often accommodated to the inequalities of the surround- ; 

 ing surface. These circumstances woidd seem to imply that the limpets are I 

 sedentary, and live on the sea- weed within reach of their tongues, or else that : 

 they retm-n 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, overgrown with nuEipores, were covered with irregular tracks, j 

 apparently rasped by the limpets in their nocturnal excursions.* i 



The limpet is much used by fishermen for bait ; on the coast of Berwick- 

 shire neaidy 12,000,000 have been collected yearly, until their numbers are so j 

 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 ; many tons weight are collected annually near the town of Larne j 

 alone (Pattison). '! 



On the western coast of S. America there is a limpet which attains the , 

 diameter of a foot, and is used by the natives as a basin (Cuming). \ 



* 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. | 



