Royal Societv.' 217 
head to the extremity of the Anus^ viz. towards the left hand op- 
pofite to the mouth, where they are acrain connef^ed together- 
One of the exterior Sranchice^ which lies upon the plain fliell, 
adheres bv its centre to the fuperior border of that large round 
muicle, which at right angles is inlerted into the middle of the 
fliells j the other exterior ^ranchice is in like manner conne61ed 
with the other head of the fame central muicle 3 from the central 
muicle thefe two exterior or fpurious Branchide confiil: of a very 
thin and pellucid membrane, and expanded to the middle of the 
fhells^ they {lightly adhere to them, fo as to become immove- 
able, and defend the back of the animal from being injured by 
the water taken into the fhellsj from this place of adhefion an 
extraordinary and thick muicle, like a border ariles, which, 
when the animal is alive is capable of great extenfion, even far 
beyond the brims of the /hells 3 it is alfo furniflied with frinaes, 
and from a reddifli colour it is variegated with very elegant 
ftreaks^ the uie of this border leems to be this 5 viz. by its ion- 
tradion inwards, like a net, when both thefe branchiated mufcles 
are darted out of the fliell, whatever prey they lay hold on, upon 
their clofing together, is for the food of the animal ; and the 
lea-water feems to be feparated by the fringes, which are in- 
dented in their extremities whilfl the food remains behind. This 
border may alio ferve for killing any fmall prey by its llron'? 
comprelTion ^ and by its undulatory motion, which is very re- 
markable, it may both retain the food, and convey it from any 
part of the circular net into the mouth, and in this manner perform 
the office of a hand. To come now to the true Sranchice^ at 
lead luch as are lb called 5 thefe are four in number, of a light 
yellow, and llriated in an elegant manner, they encompafs the 
large central mufcle, and contain between them or lie upon the 
UteruSy and its ovary, at leait on the parts ddigned for genera- 
tion. Near the mouth is a proceis wkh a double aperture, one 
of which is the outlet of the Vnlva^ and the other, if they are 
hermaphrodites, as is very probable, is defigned for the exer- 
tion of the \Peris. To proceed to the head, its mouth is fur- 
nifhed with reddijfh and very fhort lips, like the internal 'Bran- 
chide •-, about the middle of the hinge are two large circles or ca- 
vities, like the eyes of a turbot, placed obliquely. Next the 
mouth and head to the left is a large blacki/h Meconium^ behind 
that lies the heart, which may be lecn thro' its traniparent ^eri- 
cardiumy it is between a flefh colour and a reddi/h- the Aorta 
is dilinbuted into the BranchitS-^ from the Meconium arifes the 
ReElum, and pafTmg over the Pericardium', it reaches to the 
Vol. III. E e internal 
