94 MONTACUTID. 
The habitat of this singular creature is at a far greater 
elevation in the littoral zone than any other bivalve, and 
nearly as far removed from the sea-water as the Littorina 
petrea, which in many positions is never completely sub- 
merged. These minute bivalves are plentifully imbedded in 
the Lichina pygmea, and im the higher levels exist for weeks, 
without complete immersion ; they are consequently deprived 
of regular branchial currents, which in this case can only have 
a very limited operation, as in even the most favourable levels 
they must be deprived of sea-water for very many hours out 
of the twenty-four. We presume, that when these animals are 
in elevated positions, the tides washing the bases of their 
rocky habitats, combined with the saline mixture of floating 
atmospheric particles, supply sufficient humidity for the sus- 
tentation and well-being of these singular bivalves. 
MONTACUTIDA, Clark. 
Notwithstanding our disinclination to create new families, 
we have no choice but to constitute the Montacutide, though 
it be for only a single species, the Montacuta substriata, a late 
sojourner of the Kelliade. It has little in common with 
Kellia (proper), except a partial resemblance in the structure 
of the hinge and presence of a byssus, but it differs essentially 
in the absence of the singular and anomalous anterior tubular 
processes, and the probable want of a viviparous reproduction. 
With Lepton and Galeomma, both former members of the 
Kelliade, now of the Arcade, to which we refer, it has 
nothing in common but having a byssus. With Turtonia, 
also removed from the Kelliade, it cannot be associated, from 
the hinge-teeth and internal long linear white cartilage, as in 
that genus the hinge-ligament is strictly external, and the 
teeth are altogether of a different composition. No existing 
genus or family can receive M. substriata without violence to 
natural order. Therefore, as we have undertaken a new 
arrangement of the Kelliade, we are bound, as far as possible, 
in the reconstruction, to march with malacological rigour. 
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