PLEUROTOMARIID®. 73 
out with a view to ascertain the actual force with which a 
limpet clings to the rock: “It was found that limpets with 
the base one inch and a quarter by one inch—that is, giving 
an area of somewhat less than a square inch—came off at a pull 
of seventy pounds! Larger and smaller examples at the same 
proportion—that is, that the force by which they hold is 
nearly five times what would be the case if they held by 
suction only. Whether the rock was smooth (water-worn 
basalt) or somewhat rough (disintegrating granite) made no 
difference whatever.” 
W eston-super-Mare, Burnham, Clevedon, ete. ! 
PLEUROTOMARIID. 
FIsSURELLA GRECA, Linné. 
Called, by Petiver, the “thimble limpet,” possibly from its 
being open at the top, like a tailor’s thimble. 
Clevedon ! 
TROCHIDZA. 
GIBBULA CINERARIA, Linné (= Trochus cinerarius, Linné). 
Mr. Corder records it from the Burtle Beds at Perry Green, 
Wembdon. 
W eston-super-Mare ! 
GIBBULA UMBILICATA, Montagu (= Trochus umbilicatus, 
Montagu). 
Burnham ! 
CALLIOSTOMA ZIZYPHINUS, Linné (= Trochus zizyphinus, 
Linné). 
Clevedon ! 
LIT TORINIDZ:. 
Lacuna PARVA, Da Costa (=Lacuna puteolus, Turton). 
On small seaweeds at low-water mark. Jeftreys records it 
for the Bristol Channel. 
Clevedon ! 
LITTORINA OBTUSATA, Linné. 
Mr. H. Bolton records its occurrence in the shell-bearing 
gravel at Dumball Island, Avonmouth. 
Weston-super- Mare; F. A. Knight. 
About Burnham, Minehead, etc. ! 
