50 DR. G. C. BOURNE ON THE KANINID^ : 
but it is so intimately fused to the antennaiy sternum that no suture is 
visible. 
Posteriorly the mandibular epimeroii is continued into the flexible mem- 
brane forming the roof and outer wall of the branchial canal. In Notosceles 
(fig. 24) the antennary sternum is very short, is easily separable from 
the antennulary sternum, and the intersegmental arthophrragm iii/iv in 
front, and the mandibular epimera appear to be wholly membranous. In 
Lyreidiis, on the other hand (fig. 25), in keeping with the great elongation 
of the pre-oral region of the cariipace, the anterior part of the antennary 
stei-num is greatly produced and to a certain extent overlaps, but does not 
conceal, the antennulary sternum. The regions of the mandibular epimera 
are also produced far backwards on either side of the mandibular sternum 
and are calcified, but I cannot find any line of division between them and 
the antennary sternum. It should be observed that in Lyreidus the pterygo- 
stomial lobes of the carapace are produced far in front of the mandibles 
and are united for a considerable distance with the edges of the antennary 
sternum, a condition very different from that in the Leucosiida3, with which 
Lyreidus has so often been compared. 
From what precedes it is evident that the Riininidse diverge so much from 
the Dorippidse and are so much more primitive in several important par- 
ticulars, that they cannot be descended from the latter family. Nor does a 
comparison of the pre-oral segments give any support to the descent of the 
Raninidfc from the Dromiacea. Fig. 27 is a frontal view of the antennary 
and oral regions of Dromia vulgaris. The antennje and antennules have 
been removed and also the left ocular peduncle, but that of the right side is 
left in place. The whole facies is more cancroid than in the Eaninida?. The 
proximal ends of the ocular peduncles, concealed behind the inflated biisal 
joints of the antentiules when the latter are in place, are membranous. The 
antennulary and antennary fossse are small and lie in nearly the same trans- 
verse line. The orbits so far resemble ihose of the Raninidae that there are 
no downward processes of the front external to the antennules. The median 
triangular shield with the apex directed forward is the antennular sternum, 
and evidently is what Milne Edwards called the " epistome " {Joe. cit.). It 
is separated by a distinct but shallow membranous apodeme from the 
antennary sternum behind, and (here is a certain amount of mobility between 
these sterna. The apex of the antennulary sternum fits into a deep depres- 
sion of the downward process of the rostrum, but can easily be pulled out of 
it. The antennary sternum forms the anterior boundary of the so-called 
mouth-frame, and consists of a median bilobed area and two lateral wino- 
shaped areas marked off from the former by grooves. The two lobes of the 
median area are nearly square in outline and separated from one another by 
a deep median fissure : their anterior margins are thickened and truncated, 
forming a prominent ledge behind the base of the antennulary sternum. 
