114 MONTACUTID.E. 



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 

 petraa, which in many positions is never completely sub- 

 merged. These minute bivalves are plentifully imbedded in 

 the Lichina pygmaa, and in 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- 

 tentatioii and well-being of these singular bivalves. 



MONTACUTID^, Clark. 



Notwithstanding our disinclination to create new families, 

 we have no choice but to constitute the Montacwtida, though 

 it be for only a single species, the Montacuta substriata, a late 

 sojourner of the Kelliadce. 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 

 KeUiadce, now of the Arcades, to which we refer, it has 

 nothing in common but having a byssus. With Turtonia, 

 also removed from the Kelliadce, 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 Kdliadae, we are bound, as far as possible, 

 in the reconstruction, to march with malacological rigour. 



