Mr. J. Alder on Montacuta ferruginosa. 211 
connect two genera, which had previously been placed in the 
same family from the characters of the shell, but whose ani- 
mals, though agreeing in habits, presented a marked difference 
in their general appearance. The anterior part of the mantle 
in this species is ample and produced considerably beyond 
the shell, forming a kind of frill, which becomes gradually 
smaller and more even as it passes along the base of the 
shell. The exterior circumference of the mantle, lining the 
shell, is fringed with very delicate filaments, rather short and 
blunt, which extend completely round the margin of the valves, 
with the exception of a small space at the umbones. In these 
two particulars this species reminds us forcibly of the peculiar 
characters of Lepton squamosum, though they are displayed in a 
much less degree ; and we may also recognise in them a resem- 
blance to the anterior undulated portion of the cloak in the 
curious genus Galeomma, which, though distinctly observable in 
spirit specimens, I do not recollect to have seen well represented 
in any published figure. Thus then we trace a beautiful gra- 
dation of form in nearly all the genera of this family (Kelliade), 
the distinguishing character of whose animals is to be found in 
the large development of the mantle, especially in its anterior 
portion. From the largely developed cloak in Galeomma Turtom 
Gif I am right in its character, for I have not seen it alive), we 
pass to the still more developed and undulated mantle of Lepton 
sguamosum : in Montacuta ferruginosa the enlargement is chiefly 
confined to the anterior portion, which is undulated like the 
latter; in Kellia rubra the front of the cloak is still largely ex- 
tended, but the margins are even and folded into a tubular form ; 
while this part becomes an ample closed siphon in Kellia subor- 
bicularis. Taking these characters into consideration, the idea 
suggested itself, that these genera might possibly agree in re- 
ceiving the branchial currents anteriorly, as has been observed in 
the genus Kellia. For the purpose of ascertaining this pomt, I 
placed my specimen of Montacuta ferruginosa several times under 
the microscope, but without being able to make ont anything 
satisfactory. I have however since ascertained that in Montacuta 
bidentata, a living specimen of which I fortunately procured, the 
principal ingress current is decidedly anterior, though the water 
is admitted occasionally through the whole length of the open 
mantle; the exit, which was less distinctly seen, being by the 
posterior aperture. In this species a short fringe surrounds the 
margin of the shell, but during the time I was able to keep it 
alive, no extension of the mantle was observed in front ; though 
from the capricious manner in which these little animals display 
themselves, it would be premature to decide upon the absence of 
this character from a single observation. I had, on a previous 
occasion, had this species alive without seeing the fringe. 
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