REPORT OB' THE NUDIBR AN CHI AT A. 
21 
is enormously large, and measures 8 ’5 mm. in length, 10 mm. in height, and about 8 mm. 
in breadth. Its form is rather higher and shaped something like a helmet ; the 
under surface is flat ; the oblique anterior extremity of the body is narrow ; the posterior 
extremity of the body, which is also oblique, is narrow above but considerably broader 
below ; the sides of the body are divided into two halves, the anterior some- 
what convex and the posterior concave, by a keel descending downwards and backwards. 
On the anterior margin, not far from the hinge (fig. 15, b) is the pharynx (fig. 15, c); the 
sheath of the radula is not at all conspicuous on the posterior surface. The structure of 
the bulbus is quite as usual. At the opening of the labial disk were visible the margins 
of the dark brown-coloured mandibles, closely approximated to each other. — The man- 
dibles are far larger than those of any other Nudibranch. They are united to each other 
by a short, strong, tough, transverse band (above and below the small hinge). Each 
mandible was about 8 - 5 mm. long and 8 '5 mm. in height ; the thickness about the middle 
of its length was as much as 275 mm.; its colour a dull chitinous yellow, which changed 
on the lower part to a mahogany-brown, and on the antero-superior margin to a pale 
yellowish- white. The outer surface of the mandibles is convex, the inner a little concave ; 
they meet anteriorly and posteriorly in a sharp edge ; the inferior surface is very 
complicated. The outer surface (fig. 16) consists of two large facets, which slope anteriorly 
and posteriorly and meet in an oblique line or keel, which is directed downwards and 
backwards ; this line becomes fused with the outer margin of the under surface ; the 
hinder facette is in the upper part a little concave, or else very slightly convex. The 
somewhat convex antero-superior marginal part is separated from the anterior facette 
and from the upper edge of the mandible by a furrow, and as already mentioned is of a 
yellowish-white colour ; the facette itself is somewhat arched ; from its under surface 
(figs. 16, a, 17, a) is given off a powerful ridge (lying on the outer side of the 
hinge and serving for the attachment of muscles and the ligament) ; the ridge of the right 
mandible is stronger than that of the left. The inner surface is concave from above 
downwards (fig. 17), somewhat arched from before backwards; the upper marginal 
portion already mentioned is quite plain on this side ; the inner lamella of the under 
surface is fastened to the antero-inferior portion of this side. The excavated lower 
surface (fig. 18) is continued obliquely forwards and inwards into a short stout process 
(processus connectivus), which is of the same dark colour as the rest of the under surface, 
and is cut short at the extremity. The strong outer lip of this surface is depressed, 
posteriorly it diminishes in height and runs in a straight course ; the convex inner 
and outer surfaces of the lip are continued into the smooth, rounded, masticatory 
edge. The inner lip is stronger, shorter, more prominent downwards and shield- 
shaped (fig. 17, b) when seen from the inner side of the mandible, but somewhat flattened 
in the middle ; the lower margin thin, smooth. From the anterior part of the inner lip 
a convex partition wall (fig. 1 8) extends downwards obliquely to the anterior part of the 
