OPISTHOBKANCHIATA FROM THE ABROLHOS ISLANDS. 537 
Colour. The colour o£ the preserved specimen is a translucent yellow-grey, 
and Professor Dakin informs me that, in life, it was of a uniform dull yellow 
colour. 
Dimensions. The preserved example measured 22 mm. long by 14 wide 
and 9 mm. high. 
Head. The head is flattened and covered by the forward extension of the 
mantle. It bears a strongly developed oral veil, and this is continued out 
laterally into two short triangular expansions, which represent the oral 
tentacles and are deeply cleft along their lower outer edge. The mouth is 
a round opening under the head, and between it and the anterior extension 
of the foot. 
Foot. The foot is well developed, and, although fairly broad, it is overhung 
along the sides of the mantle, but probably the posterior end is free during 
locomotion. The anterior end is abruptly rounded and carried on beyond 
the mouth as a shallow flange, and the posterior end is bluntly pointed. 
Rhinophores. The rhinophores are well-developed cylindrieo-conical 
structures lying under the front end of the mantle at the hinder dorsal region 
of the head. They arise practically touching one another in the middle line, 
but diverge slightly as they pass forwards and they are deeply sulcate on 
their outer margins. Just behind the base of each a well-marked, dull black 
eye-spot shows through the skin of the neck. 
Gill. The gill is situated well forward on the right side of the body under 
the mantle. It is attached at the front or basal end and passes backwards as 
an elongated pyramidal structure, bearing' about 24 lamellae on each side of 
a smooth rachis. 
Shell. The shell was, unfortunately, too damaged to admit of accurate 
description, but it appears to be verj' similar to that of Bertliella [Pleuro- 
hranchus'] plumula as described and figured by various authors. 
Labial Armature. The labial armature consists of two oblong plates 
measuring 3 mm. long by l"5mm. wide. They are of a horn-brown colour 
and are composed of tooth-like elements. Each consists of a lanceolate 
flattened blade coming to a single, sharp, non-denticulate point, and bears, 
some way down on each side, a blunt triangular process, but these two 
projections are not opposite to one another. The elements agree with those 
figured by Bergh (27) and Vayssiere (75). 
Radula. When flattened on a slide the pale yellow radula measured 4 mm. 
by 2 mm. It has no rachidial teeth and the pleural teeth are arranged in 
78-82 rows ; a typical row contains 280-290 teeth and the formula is 
(140-14.')) . . (140-145). The teeth increase in size from the rachis out- 
wards, reaching their maximum well beyond the middle line ; they then 
decrease slightly, but the outermost teeth, although slender, are still longer 
than the innermost. All the- teeth are of very similar shape and stand 
practically upright. They have a small base, from which conies off a long 
