50 
THE VOYAGE OE TI.M.S. CHALLENGER. 
occupies its usual position beneath the second interbranchial space ; from it projected 
the conical glans penis, which attained a length of 4 mm. The anal papilla and the 
minute renal pore are situated beneath the fourth interbranchial space. The foot 
resembles that of other Marionice, the free margin projecting about 1*75 mm.; the tail 
measured about 2‘25 mm. in length, and had a triangular crest 2'25 mm. in height. 
The viscera are not visible through the body-walls. 
The central nervous system is small ; the cerebro-pleural ganglia (PL XI. fig. 3, a, b) 
are reniform in outline, and the two divisions are quite distinct, and the anterior is 
somewhat larger. The cerebro-pedal and pleuro-pedal connectives are very distinct ; 
the nervus vaginae rhinophorii, nervus olfactorius, nervus tentacularis, nervi frontales, 
nervi palliales, nervi musculares bulbi, nervus opticus and ganglion opticum resemble 
those of other Tritonice. The pedal ganglia (fig. 3, c,c) are rounded and short stalked, they 
are a little larger than the cerebral ; the nervi pediaei as usual. The olfactory, buccal 
(fig. 3, g), and gastro-oesophageal ganglia (fig, 3, hh) are like those of other Tritonice. 
The eyes (fig. 3, i) are situated as usual at the base of the rhinophorial sheath ; they 
are oval in form, about - 22 mm. in diameter, and are provided with a large lens and black 
pigment. The large otocysts (fig. 3) are placed either behind or upon the pleuro-pedal 
connective; each contains about 100 otoconia, the largest of which have a diameter of 
*03 mm. 
The mouth-tube with its retractor muscles was quite typical. The bulbus pliaryngeus 
measured 10 mm. in length, 6 mm. in height, and 7 mm. in breadth ; it is not different 
from that of other species of Marionia ; as in Marionia quadrilatera, the black, deeply 
pigmented wall of the buccal cavity was visible on the upper surface of the bulbus. The 
labial disk is whitish in colour. The mandibles (PL XI. fig. 4) correspond in measure- 
ment with the bulbus pliaryngeus. Their colour is chitinous yellow ; in shape they are 
closely similar to the mandibles of other species of the same genus, differing merely in 
being somewhat narrower, and in having a more pointed posterior extremity ; the masti- 
catory process (fig. 4, a) is long, the masticatory edge (figs. 5, 6) straight and armed along 
its whole length with three or four series of denticles, the highest of which measure 
about - 12 mm. The tongue is of the usual form; the radula, of a chitinous yellow 
colour, stands out in marked contrast to the rest of the organ, which is black. The 
radula contains forty series of teeth (counted along the outer margin) ; further back, 
beneath the tectum radulse and within the radula-sheath, there are eight fully-developed 
series of teeth, one half-developed, and three delicate transparent series ; the total num- 
ber of series of teeth is thus fifty-two. The greatest number of teeth contained in one 
of the anterior series of the sheath was eighty, but nearly all the series of the tocgue 
were incomplete. The breadth of the oldest median teeth was '28 mm., of the newest 
•39 mm. ; the length of the outermost plates on the posterior portion of the radula was 
•12, '16, '2, and ’25 mm., the longest measured as much as *4 mm. The median teeth 
