76 ARCADE. 



The foot is hyaline azure, with a broad longitudinal medial 

 line of intense snow-white, and a still intenser flake at the 

 anterior end ; it is fixed to the centre of the body by a mode- 

 rately long pedicle; on first protrusion it takes a vertical 

 position, and has a linguiform tapering aspect, but this part 

 almost immediately, after feeling about, ranges itself anteriorly 

 and horizontally ; and at the same time, on the other side of 

 the pedicle, a bevelled, attenuated, pointed portion issues, 

 somewhat shorter than the first ; this is longitudinally cloven 

 as far as the pedicle, and can form a sort of oval disk, but on 

 the march it is rarely expanded : at the base of the cleft is 

 the byssal gland, which occasionally pours out a glutinous 

 red filamentous matter, that in confinement is copious, and 

 discharged anteriorly, which at first I thought was faecal 

 matters, and was puzzled to account for such an issue anteally, 

 but the subsequent view of the single sessile posteal anal 

 conduit and the ejection of pellets cleared up the difficulty. 

 This foot is in every respect similar in miniature to that of 

 the Pectunculus pilosus and of the Arcada, and in no other 

 bivalve family does the foot exhibit a similar structure : this 

 singular pedal characteristic of itself would sufficiently confirm 

 the natural position of Lepton and Galeomma. 



The animal is vivacious, and allowed itself to be examined 

 many times daily ; it marched with quickness, but I only once 

 saw it progressing in a vertical position ; the usual posture of 

 the shell is to rest on one of the disks, which is frequently 

 changed for the other ; the adductors did not appear to allow 

 of a greater opening of the valves than the ordinary extent. 

 The animal, when placed at the bottom of a glass, always 

 crawled up and moored itself by a filament at the side ; some- 

 times, however, it slipped its moorings and floated free on the 

 surface of the water with the umbones downwards, and after 

 an interval refixed itself by spinning a byssal thread. 



I cannot speak at present of the branchiae and palpi, as the 

 animal and shell are in my collection, and are thus preserved 

 to show that the shell, though usually described by concho- 

 logists as gaping, can, in consequence of the flexibility of 

 the thin laminar valves, be completely closed. There is no 



