182 A IIISTORY OF RECENT CRUSTACES 
calcareo-membranous chamber, attached to the upper wall 
of the antennz. Around the orifice that opens into it, 
within the chamber, there is a curved row of closely 
planted delicately ciliated hairs, each of which is attached 
to the base by a flexible membranous articulation, from 
which it proceeds flattened and tolerably broad for more 
than half its length, when it narrows rapidly and becomes 
ciliated, the cilia being short and fine; the hairs extend 
nearly if not quite across the auditory chamber, the floor 
of which is covered with small points, while the cavity 
contains much angular calcareous sand. This I found 
mostly gathered into a compact mass, but most probably 
when the animal was in a living condition it was not so, 
being then kept in a state of motion by the aid of the long 
slender ciliated hairs that have just been described.’ In 
discussing the peculiar combination of slender filaments 
and flattened plates in the branchiz of this crustacean, 
Mr. Spence Bate observes :—‘ In a respiratory chamber, 
such as in the genus now before us, the water flows in by 
the posterior extremity, for which purpose the carapace 
can be raised or depressed at will within certain limits; 
and as we may assume that in a large chamber such as 
the present, the water flows along the lower margin, pass- 
ing out at the anterior end only, it is probable that the 
largest amount of current will correspond with that por- 
tion of the chamber where the trichobranchiate filaments 
are best developed and most abundant, whereas the phyl- 
lobranchial plates are present in the centre and deeper 
recesses of the chamber, where the circulation will be 
more quiescent, and the power of oxygenation less effi- 
cient.’ As there is reason to suppose that the animal may 
inhabit hollow passages in the mud, where the circulation 
of water through the branchial chamber would not be very 
vigorous, and least so in the part most distant from the 
direct current, Mr. Spence Bate infers that in the central 
portion of the chamber the branchiz have been developed 
into thin foliaceous plates of considerable dimensions, so 
that through the tenuity of their structure the blood may 
be brought over a large surface into contact with the 
aerating medium within the chambers. 
