SOLEN. 153 



there are about fifteen, and in the upper, thirty of different 

 sizes. The foot is long, strong, muscular, and subcylindrical, 

 fixed to the comparatively small body about the middle of the 

 shell ; it has the power of changing the terminal portion into 

 all shapes, from the fine elongated tentacular point, to the 

 decided club-shaped extremity ; the foot, when half-extended, 

 is oblique, and obtusely pointed; the colour is pale yellow- 

 white, marked for some distance anteally with exceedingly 

 fine, very pale, close, lead-coloured lines. 



The animal has two systems of locomotion; the one for 

 ascending from its deep perpendicular hole, the other for 

 changing its locality, which it can effect by darting forward 

 with a rapidity equal to that of the Pectines. The foot has a 

 decided tubular aquiferous canal, from its junction with the 

 body to within a short distance from the termination; the 

 outer tissue appears homogeneous, but the entire conical cavity 

 is furnished with strong elastic fibres, which doubtless have 

 the power to close or greatly contract it. How the water 

 gets access to the cavity is doubtful ; I could detect no orifice 

 either at the point or junction with the body; one must 

 suppose it to enter by the mouth, stomach, and walls of the 

 crystalline stylet, and, from thence, to have a contact with the 

 enveloping membrane of the viscera, if not an inward com- 

 munication. What is the particular O3conomy of this sort of 

 foot, which is in some measure analogous to that of the 

 Lucina, only in them it is perforated throughout, is at pre- 

 sent hypothetical. Can it be, in Solen, to give it increased 

 power and elasticity, and in its deep hole of two feet or 

 more, by a sudden compression to aid the muscular extension, 

 which alone could not effect the ascent of the animal from its 

 deep lodgement ? and is the compressive action also the agent 

 to enable it, when out of its retreat, to dart with such unusual 

 rapidity ? 



There are on each side a pair of equal-sized, long, linear, 

 narrow branchiae, which, after getting rid of the interposition 

 of the body, proceed, fixed to the roof of the long dorsal range 

 of the mantle, to the branchial siphon, each pair united to 

 the other, to deposit in it their attenuated points, as in the 



