56 OSTREAD 2. 
nates. There are on each side a pair of simple branchiz that 
are without the reflected pouches of Pecten, nearly of equal 
depth, closely and conspicuously striated on both surfaces ; 
they extend anteriorly to the palpi, but posteriorly only reach 
a little above the ventral range; with them are connected 
around the mouth, by plain labial cords, two pair of subtri- 
angular, moderately long and large palpi, each plate being 
hung separately to the body, as in the ordinary Bivalves ; they 
are smooth on the outer surfaces, and well pectinated within ; 
the plates of each pair lie one on the other, but not bemg 
attached laterally, they do not double as a book shuts, or like 
those organs in Pecten. The body has not the rudiment of 
a foot; the animal is, I believe, deprived of all locomotion ; 
when the shell is not free, it is fixed by the under, which is 
the convex, valve. 
This species, when it inhabits the crevices of rocks, is sub- 
ject to great distortion; but the animal, though the shell 
forms a cylinder, or a right angle, or a disk, flatter than that 
of a Placuna, adapts itself to these irregularities. There is 
but one British species, exhibiting infinite varieties, the effect 
of habitat and cultivation. 
The stomach contains the attritor or tricuspid appendage, 
that is worked by a short, grooved, elastic stylet, which, as 
there is no foot, has a resting-place in the upper part of the 
body. The intestine pierces the body to its fundus, then 
ascends, passing the heart without contact, which is one of 
the exceptions to the almost universal position of that organ 
in the Acephala; it then issues at the upper part of the 
dorsal slope, from which point it coasts in view, and is glued 
to the great adductor, terminating in a short, floatmg rectum 
nearly at the ventral level. The ovary appears to be amal- 
gamated with the body, and from April to July is contimually 
discharging the ova into the branchie, where they remain 
until they are ready to be replaced by another batch, and so 
on, until all are committed to their natural habitat ; then the 
animal recovers its exhaustion, and is edible about the middle 
of August, but is not considered fat and in full flavour until 
September. 
