Mr. W. Clark on the Animal of Kellia rubra. 143 



branchial currents is a sad mistake ; nothing can be more irre- 

 gular, capricious, and uncertain ; they depend entirely on the 

 volition, habits, and wants of the animal, and are often suspended 

 for weeks in Kellia rubral and twice in every twenty-four hours 

 in the mussels and numerous Gasteropoda inhabiting the higher 

 levels of the littoral zone. 



I positively dissent from Mr. Alder's views, repeated in his 

 last paper, that the open fold of Kellia rubra is a special bran- 

 chial organ. That the water enters therein no one disputes, inas- 

 much as this fold is a simple continuation of the ventral portion 

 of the mantle, and the water must flow therein, as it does in 

 every other part of an open mantle. This sentiment is a repe- 

 tition of one in a former paper ; but it is necessary to keep it in 

 view, to show that the fold in question has no pretensions, as I 

 think, to be considered as a special branchial organ to supply the 

 want of one in the usual place nature is always accustomed to 

 fix it, and I am inclined to think that Mr. Alder will ultimately 

 find that she has not, as he states, placed the " inhalant siphon " 

 " before instead of behind." 



This idea of inverting the invariable order of nature to account 

 for an anomaly in the structure of Kellia rubra is a stretch of 

 imagination, far beyond my conjecture, that the fold in question 

 may be to assist locomotion. But I shall not be surprised to find 

 that Mr. Alder and myself have mistaken the use of this fold in 

 Kellia rubra, and that it may minister to supply water to the 

 viviparous colony deposited in the ovarium of the animal of this 

 species, and also act as an oviduct and receptacle for the young, 

 until they are sufficiently developed for exclusion. This idea 

 arises from having seen, when examining some Kellia suborbicu- 

 laris in a saucer, several testaceous young ejected from the ano- 

 malous tube of one of the animals, which I find, as Mr. Alder 

 states, is entire, and not an open fold as in Kellia rubra ; these I 

 immediately gathered up, and have them now by me. I men- 

 tioned some time ago this circumstance to Professor Forbes ; 

 but notwithstanding this fact, I have never been able to dis- 

 cover, in any of the very numerous ovaria of this species I have 

 examined, anything but ova, but it is exceedingly probable the 

 shells I saw ejected may have been deposited in the curious and 

 extraordinary appendage in this animal, and there received the 

 development in which I found them. 



As to Mr. Alder's other observations, on some quotations from 

 my last paper, I leave them as I find them. 1 really have some 

 difficulty in appreciating their scope, aim and applicability ; in- 

 deed some of them are so involved as not to be clear. I therefore 

 beg him to accept the following new demonstration of the fallacy 

 of the inhalant and exhalant branchial currents in the bivalves 



