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 [Kelliadce), 

 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 Turtoni 

 (if 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 

 squamosum : 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 point, I 

 placed my specimen of Montacuta ferruginosa several times under 

 the microscope, but without being able to make out 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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