56 OSTREADJE. 



nates. There are on each side a pair of simple branchiae 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 being 

 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, floating rectum 

 nearly at the ventral level. The ovary appears to be amal- 

 gamated with the body, and from April to July is continually 

 discharging the ova into the branchiae, 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. 



