of the Bivalve Mollusca. 245 
while another flows off posteriorly near the termination of the 
branchie*. 
I now come to the most interesting part of Mr. Clark’s letter, 
where he informs us that he has ascertained that Kellia subor- 
bicularis is viviparous,—a good discovery: but the supposition 
that the anterior siphon is only intended as a marsupial pouch 
for the further development of the ova after their extrusion from 
the ovarium, is a conjecture not warranted by Mr. Clark’s own 
observations, as he afterwards saw completely testaceous young 
in the ovarium, thus doing away with the necessity of their 
being further detained in the open siphon, which is ill-adapted 
to the office assigned to it. Besides, if such had been the case, 
it would most likely have been observed before, as from the 
hyaline transparency of the tube and its wide aperture, it is 
always easy to see to the bottom of it. That the young escape 
by this aperture is probable, but this does not prevent its being 
used for branchial purposes ; as in no instance that I am aware 
of, either in a Bivalve or an Ascidian, is there a separate orifice 
of the cloak set apart for the extrusion of the ova. All that can 
therefore be admitted as proved by Mr. Clark’s observations, are 
the viviparous character of the reproduction im Kellia suborbi- 
cularis and the escape of the young (in one instance at least) by 
the anterior siphon. May I not add,—it is also proved by equally 
authentic observations, often repeated,—that both in Kellia rubra 
and Kt. suborbicularis, a special current can be seen to go into 
this siphon, and at no other part of the circumference of the 
mantle ? 
I remain, dear Sir, yours very truly, 
JosHua ALDER 
P.S. Since writing the above I have had an opportunity of 
examining the currents in Pholas crispata, which I find to cor- 
respond entirely with those of the species already mentioned. 
As however Mr. Garner, in his excellent paper on the Lamelli- 
branchiata, though agreeing in the general existence of ciliary 
currents received and expelled by separate apertures, yet consi- 
ders this and some other allied genera to be exceptions, I pur- 
pose, with your permission, to treat this part of the subject a 
little more at large in a separate communication. 
* With respect to the range of Kellia rubra, Mr. Clark has ascertained 
that he was right in stating that near Exmouth this species is found beyond 
ordinary high-water-mark, and often, in calm weather, is only covered by 
the sea at spring tides. If it has been also ascertained that “ thousands of 
these animals pass their entire existence without perhaps being completely 
in a condition to receive branchial currents of sea-water,” I shall agree 
that I was mistaken in thinking the account in question overstated. ‘The 
ordinary range of Kedlia rubra is within tide-marks. 
