A STUDY IN CARCTNOLOGY. 37 
and second pereiopods are almost ventral. Thus, in the middle of the thoi'ax, 
the articular sockets o£ the limbs have the same position as in the Astacura, 
but at the two ends their position is similar to that seen in crabs (PI. 5- 
fig. 17). The epimera of lianina arc of great depth and exhibit peculiar 
features that will be described later ; for the moment it is sufficient to note 
that, owing to the size and depth of the epimera, the arthrophragais are 
relatively short and as in the Astacura are somewhat narrow curved luminse 
separating the articular cavities. But, as also in the Astacura, the arthro- 
phragnial apodemes are deeply extended into the body for a limited space on 
either side of the mid-ventral line. These extensions are the so-called endo- 
stcrnites, and in all the Raninidaj they are very largely developed, the largest 
of them, namely the intersegmental jiair xi/xii, extending upwards as much 
as two-thirds of the entire depth of the thorax. As may be seen in PI. 4. 
fig. 9 and PL 6. fig. 16, the four posterior pairs of endosternites slope 
sharply forwards from their points of origin from the arthrophragms, but the 
intersegmental pair ix/x stands nearly vertically and the pair next in front 
slopes somewhat backwards. The upper ends of the endosternites are widely 
expanded, and their innermost expansions, the mesophiagms of Huxley, 
unite in the middle line to form the roof of a very well-marked and vory 
deep sternal canal, at the bottom of which lies the ventral nerve-ganglion 
chain. This is a wholly Macruran character and, as we have seen, it is 
unrepresented in Dromia. In this respect, therefore, as in the nervous 
system, the Dromiacea have departed further from the Astacuran and have 
advanced further towards the cancroid type of structure than have the 
Raninidse. The former cannot be in the direct ancestral line of the latter. 
To return to a consideration of the epimeral elements of the thorax. The 
epimera (fig. 17), with the exception of the last thoracic, have a great 
extent dorso-ventrally and present features absolutely distinctive of the 
Raninidse. That of segment ix stands nearly vertical and the broad 
epimeron of segment x nearly so. These two do not present any specially 
abnormal features, but the three succeeding epimera slope sharply forwards, 
so that their upper extremities converge towards the upper posterior angle 
of the tenth epimeron, and their extensive lateral surfaces are divided into 
dorsal and ventral moieties by a ridge running obliquely upwards from the 
hind margin of the articular cavity of the cheliped to the insertion of the 
abdomen. Against this ridge the lower edge of the branchiostegite fits 
closely and is held in position, by two projections, one near the anterior edge 
of the eleventh, the other at the posterior edge of the thirteenth epimeron, 
just in front of the articular cavity of the last pereiopods. The lower moieties of 
the epimera of the eleventh, twelfth, and thirteenth segments are therefore 
exposed on the surface, and form a somewhat excavated and roughly quadri- 
lateral area between the coxse of the limbs and the brancliiostegite. The 
