A STUDY IN CARCINOLOGY, 49 
and tlie anlennary sockets lie well liehind the ocular peduncles ; there ai'e no 
antennulary fossse internal to the orbits. The ocular peduncle o( lianiiia, as 
is well known, exhibits these calcified segments bent at an angle to one 
another when the peduncle is retracted into its orbit. Reference to fig. 22 
shows that there are similarly three segments in the ocular peduncle of 
Notopus, but the two proximal are very short, the greater part of the 
peduncle being formed by the elongated distal segments which, when turned 
backwards and downwards, rests in an elongated orbital excavation fringed 
with hairs. There is no division of the orbit by a downward growth of the 
front external to the antennules, and the proximal segments of the ocular 
peduncles are inserted close to the middle line on either side of the rostral 
dovvngrowth. In all these respects the Raninidas have departed very little 
from the Astacuran type and differ from the more cancroid characters 
exhibited by the Dorippida3. In Notopus the downward process of the 
rostrum is narrow and strongly keeled ventrally ; its dovetail-like articu- 
lation with the aiitennulary sternum is well seen in fig. 22. The antennulary 
sternum is escutcheon-shaped, strongly keeled in the middle line, and narrow 
posteriorly. It has a certain amount of mobilit}' on the antennary sternum, 
which latter structure is a broad triangular or rather V-shaped plate the 
apex pointing forward, the antero-lateral margins raised and thickened but 
not infolded and forming part of the inner wall of the autennary sockets : 
more posteriorly these margins are united to the pterygostomial lobes of the 
carapace. The ventral surface of the antennary sterjium is deeply excavated 
to form the exhalant orifice of the branchial canals ; its anterior moiety is 
divided into right and left channels by a low median ridge, posterior to which 
the right and left branchial canals are separated from one another b}' a large 
ventrally projecting hood. This hood, which is characteristic of the Rani- 
nidfe, is the greatly developed median part of the mandibular sternum, and its 
postero-external corners are produced right and left into curved horns at the 
extremities of which are the strophidia for the articulation of the mandibles. 
The suture between the antennary and mandibular sternum is well marked 
in all the Raninidse I have examined. The shape and size of this hood-like 
mandibular sternum and its relations to the antennary sternum in front and 
the labrum behind are shown for Ranina in the perspective sketcli (-fig. 26). 
The figure also shows the curved lines of hairs guarding the exit of the 
branchial canal ; the posterior and more prominent line of hairs marks off 
an oblong plate forming part of the roof of the branchial canal, and as a 
distinct suture can be observed internally corresponding to the external line 
of hairs, I identify this oblong plate with the mandibular epimeron. In 
Notopus the exit of the branchial canal is guarded by a diffuse hairy 
patch, and the area behind this, drawn out into the triangular projection 
shown in fig. 22, must be taken to represent the mandibular epimeron, 
LINN. JOUEN. ZOOLOGY, VOL. XXXV. 4 
