Mr. J. Alder on the Animal of Kellia rubra. 53 



that she has not departed from her usual scheme^ and that this 

 fold is not a special branchial organ, but is intended to fulfill 

 other functions.'^ is this a legitimate conclusion to arrive at ? 

 Mr. Clark here argues as if the departure from the usual scheme 

 in Kellia rubra was in having a special branchial orifice ; but this 

 is not the point of difibrence, as I have before stated, and these 

 objections, if they have any weight, must apply equally to the 

 posterior branchial siphons of all the open- mantled bivalves. 

 They all have a pedal aperture through which the currents can 

 enter. What then is the use of the so-called branchial siphon ? 

 Or why are there three apertures performing the same function ? 

 Surely there is something very like surplusage here. The " cui 

 bono '' may well be asked of Mr. Clark's views, but not of mine, 

 as I assign a separate function to each orifice : the branchial one 

 being kept apart from the opening for the foot in order that the 

 currents may not be interrupted by the action of that member. 



But Mr. Clark says, the foot does intrude itself occasionally 

 into the folded siphon of Kellia rubra ; and this is the last and 

 " conclusive proof '' by which I am to be put hors de combat, 

 " The animal very often thrusts its foot into the fold, and by the 

 withdrawal of which it is opened and the edges separated. How 

 then can a fold, whose form by this action is continually changing, 

 and is subject to momentary/ interruption, be the conduit of re- 

 gular, delicate, and uninterrupted currents V I would ask, does 

 not this objection tell more strongly against the true pedal 

 opening of this and other bivalves, which Mr. Clark wishes to 

 make out is the principal one for the entrance and exit of 

 branchial currents ? Let any one look at this little animal with 

 its siphonal fold stretched out in front, and frequently expanded 

 almost into a cup-form, as if courting the entrance of the vivifying 

 stream, and then say whether the basal part through which the 

 foot is constantly protruded when in action, or the siphonal fold 

 into which it not unfrequently makes a momentary incursion, is 

 most free to supply the currents necessary for respiration and 

 food. Mr. Clark calls these currents " regular, delicate, and un- 

 interrupted." I have said that they are continuous, and pretty 

 regularly sustained, but never contemplated asserting that they 

 were not liable to occasional or accidental interruption. 



I shall now briefly advert to the curious use which Mr. Clark 

 has found for the siphonal fold as a prehensile organ, and the 

 no less curious terrestrial habits which he supposes this little 

 bivalve to possess. For both T think that gentleman is greatly 

 indebted to a lively imagination. Probably he will also find, 

 on a more careful examination, that its habitat beyond tidal range 

 has been rather overstated. I have never foimd it but within 

 tide-marks, and cannot conceive how a bivalve mollusk, whose 



