on one fide of immoderate fize, while thofe of the 
oppofite fide are thin and fmall; and in fome par¬ 
ticular fpecies, as the C: vocans, &c., the fize of 
the large arm is fo great as to oblige the animal to 
fupport it on its back, in which pofition it is gene¬ 
rally placed while the creature is walking. It may 
likewife be added that this is a particularity which 
is fometimes reverfcd; a circumftance which takes 
place, as is well known, in the univalve fhells. 
