54 
THE YOYAGE OF H.M.S. CHALLENGER. 
containing a number of large vesicular glands ; in the neighbourhood of the apex were a 
number of special glandular structures (fig. 21), which appeared to resemble renal 
tissue ; the condition, however, of this part of the body hindered further research. 
The wide mouth-tube measures about 1*5 mm. long. The stout bulbus pharyngeus is 
about 2 mm. long, 1*75 mm. broad, and 1*5 mm. high ; the radula sheath projects a little 
beneath at the hinder end ; the form of the bulbus is nearly as usual, but peculiarly 
flattened on the upper surface ; within the oval labial disk were the dark brown edges of 
the mandibular plates, the upper transverse pieces of which were visible through the 
walls of the bulbus. The mandibular plates (fig. 10) resemble those of Polycera 
quadrilineata, they are strong and hard, and yellowish in colour ; the length of the 
longitudinal piece *75 mm., of the transverse piece *1 mm.; they consist of two parts 
inclined to each other at nearly a right angle (fig. 10). The longitudinal piece (fig. 10, b) 
mainly lies naked in the labial disk, and is sickle-shaped ; the anterior surface is 
rather convex, marked with several oblique lines, reaching above as far as the junction ; 
the outer margin is strongly projecting, separated by a deep furrow from the transverse 
piece ; the hinder surface is a little concave, reaching as far as the junction, and passes 
into the transverse piece by means of a rounded crest ; the inner margin is a little 
convex above ; the under end brought to a point. The transverse piece (fig. 10, a) of the 
mandible is scarcely longer but (especially behind) broader than the longitudinal ; it 
lies nearly horizontally, but sloping downwards slightly in its anterior portion ; the upper 
side is a little convex, and traversed by an oblique longitudinal crest ; the under side is 
rather concave ; from the (fig. 10) inner portion of the upper margin, quite separate from 
the hinder surface, a flat piece takes its rise, which extends backwards, and becomes 
attached to the inner margin of the longitudinal piece ; there is a deep furrow between 
this flat extension and the longitudinal piece, and also between it and the transverse 
piece. The structure of the bidbus pharyngeus is as in Polycera. 1 The tongue is as usual, 
broad and strong ; the chestnut-coloured radula is visible through the upper wall of the 
bulbus, and contains eight rows of teeth ; further back there are three developed and one 
undeveloped rows, the total number is therefore twelve. The first row of the tongue is 
reduced to the inner lateral teeth, but the following series is complete ; the lateral teeth 
of this and the following rows were somewhat worn out. The teeth had a dirty yellowish 
or brownish-yellow colour. The length of the outermost tooth on the hinder part of the 
tongue was about *1 mm., of the next plate *14 mm. ; the innermost lateral plate 
measured *2, and the large one as much as *3 mm. Therhachis (fig. 11, a) is rather broad, 
and traversed by wavy folds. The two lateral teeth, rather similar in shape, have a 
flattened basal portion, and a powerful smooth hooked extremity ; from the outer margin 
of the body arises a strong wing-shaped process. The inner lateral plate is smooth, and less 
Bergh, Beitr. zu einer Monogr. d. Polyceraden, I. Verhandl. d. k. 7c. zool.-bot. Gesellsch. Wien, 1879, Bd. xxix. 
pp. 60G, 607. 
