A STUDY IN CARCINOLOGY. 63 
that in the Raninidse an anterior iucurrent stream of water is produced by 
the "normiil" action of the scaphognathite. 
In no other member of the group (witli the possible exception of Cosnio- 
notus, which I have not had the opportunity of studying sufficiently closely) 
do the flagella of the antennte form a water-tube as in JSfotopus and Ranilia. 
Indeed, the antennas are modified in other directions but, none the less, are 
subservient to the establishment of an inhalant water current, the course of 
which can best be described by taking lianina as an example. 
In this genus both the antenuie and the antennules are modified in con- 
nection with the respiratory currents. The antenna (figs. 35 & 35 a) is short 
and thick, the flagellum reduced to a rudiment comprising at the most seven 
joints ; often it is missing. The two basal joints of the peduncle are fused 
together, but the suture between them remains distinct. The first joint is 
triangular in outline, with the apex directed forward ; its admedian basal 
angle projects inwards and slightly forwards and the excretory aperture is 
placed somewhat to its dorsal side, in such a' position that the e xcretory 
products are discharged into the excurrent rather then into the incurrent 
' stream. The two basal joints, which have a very limited movement in the 
antennary socket, lie directly in front of the sub-antennary lobe of the 
pterygostome, but the third peduncular segment is flexed inwards to form a 
somewhat acute angle with them. The shape of the third segment can best 
be understood by reference to figs. 35 and 35 a, \\ hich represent external and 
admedian views of the right antenna. The most noticeable feature is the 
great development of the external lobe. Small and inconspicuous in Notopus, 
this lobe in Ranina forms a large sinuous ridge which projects forward as far 
as the anterior limit of the fourth segment ; its outer margin is fringed with 
long plumose setse. When the third peduncular segment is flexed towards 
the middle line, the lobe in question is brought into a position athwart the 
incomplete lower boundary of the orbital cavity, and. forms its ventral and 
internal wall, the long fringe of hairs on what is now its anterior maroin 
extending upwards across the orbital cavity and interlocking with a similar 
fringe spreading downwards from the supra-orbital ridge of the front of the 
carapace. For brevity's sake this lobe will be referred to as the crest of the 
third peduncular segment. The fourth segment is sub-triangular in section : 
its external and ventral surfaces are convex and granular, but its internal 
surface is smooth, slightly concave, and flabelliform in outline. Its maroins 
are surrounded with long plumose seta; the disposition of which is shown in 
fig. 35 a. The fifth peduncular segment is small and the flagelkim rudi- 
mentary or absent. When the antennae are flexed inwards, the concave 
flabelliform surfaces of the fourth segments are brought nearly into contact 
in the middle line, their marginal setse interlock, and thus a narrow but deep 
space is enclosed which is continued posteriorly into the wider space bounded 
