4(3 DR. G. C. BOURNE ON THE RANINID.^E : 
narrow transverse bar at the base of the rostrum with [the tergnin of the 
ant.ennnlary segment. This bar is easil}' seen from the inside, but does not 
appear in a front view, being concealed by the base of the rostrum. Right 
and left of it are two deep crescentic grooves which are the external indica- 
tion of two deep aliform a]5odemes to which the anterior gastric muscles are 
attached. The apodemes in question are known -as the procephalic lobes, 
and various suggestions have been made as to their significance, but, in my 
o|)inion, they are simply the well-developed pleural apodemes of the inter- 
segment i/ii. Thus far the interpretations I have given are hardlj', if at 
all, at variance with those of previous authorities, but the homologies. of 
the antennary and mandibular segments present greater difficulties. The 
so called epistome of Neplirops, as also that of the lobster and the craj^fish, 
is clearly made up of two parts : an anterior broad plate the lateral regions 
of which are produced right and left into broad divergent wings, giving the 
whole the shape of a broad inverted V. Behind this, fitting- closely into 
the angle of the V, but separated from it bj^ a distinct groove, is a somewhat 
projecting narrow curved bar the outer extremities of which end in incurved 
knobs, which knobs are excavated internally to form the strophidia for articu- 
tion with the inner articular processes of the mandibles. The presence of 
these strophidia is of itself evidence that the bar in question is the mandibular 
sternum. The transverse groove in front of it deepens in the middle line to 
form a triangular pit or depression and on the inner surface is a correspond- 
ing projection— in fact, an apodeme for the attachment of muscles. As 
transverse apodemes are always intersegmental, this groove with its median 
apodeme indicates clearly enough the boundary between the antennary and 
mandibular sterna. The autennar}^ epimeron of either side is represented by 
the very narrow curved bar forming the outer boundary of the antennary 
socket. This bar is united by a membranous fold to and is overlapped by 
the fold of the anterior margin of the carapace forming the commencement 
of the branchiostegite. Posteriorly this bar bends inwards to form the 
thickened interned rim of the antero-lateral margin of the antennary 
sternum, and though it is completely fused with the latter, I do not doubt 
that this thickened rim represents the intersegmental arthrophragm ili/iv. 
Externally the antennary epimeron expands and passes, without any obvious 
line of demarcation, into the calcified plate marked x in fig. 18. In 
Neplirops this plate is firmly fused to the outer edge of the V-shaped 
antennary sternuni, and is set back at an angle to it in such wise as to form 
the inner and upper wall of the anterior part of the exhalant branchial canal, 
but in both the lobster and the crayfish it lies more nearly in the same 
plane as the antennary sternum and takes little or no part in the formation 
of the branchial canal. The postero-internal margin of this plate is thickened, 
produced backwards, and engages in a groove on the front surface of the 
