28 
THE VOYAGE OF H.M.S. CHALLENGED. 
band ; on the posterior half of the back, below on the side of the body, and on the edge 
of the foot, there were a number of small partly white rounded oval spots, regularly 
arranged ; the margin of the foot is whitish ; the hepatic cseca are visible through the 
walls of the papillae, and are brown or black. 
The shape of the body is slender, like that of other specimens of the genus. The 
mouth-tube was invaginated ; the strongly developed tentacles are sharply marked off from 
the rest of the head; the rhinophoria are cylindrical in shape and provided with about 
fifteen rings, and here and there half rings lying between the others. The naked part 
of the back is about double the breadth of the portions covered with papillae ; the breadth 
of the back decreases towards the hinder end, but the relation between the portions of 
the back covered with papillae and the uncovered portion remains the same. On the 
lateral portions of the back the papillae are arranged in six low horse-shoe-shaped cushions, 
and further back there are three isolated rows. The size of the cushions themselves, and 
of the intervals between them, decreases from before backwards. The anterior leg of the 
first 4-5 horse-shoes is stronger. The, first horse-shoe-shaped group of papillae has the 
anterior portion much thicker, and provided with about eight series of papillae ; the 
hindermost has only two rows. The second group is smaller, but the anterior portion of 
it is in the same way thicker, and has five or six rows of papillae, the posterior portion 
only having two. At the upper end of the corner of this horse-shoe is the somewhat 
conspicuous anal papilla inclining towards the posterior leg. The renal aperture is more 
anterior, and a little lower down. The third, fourth, and fifth “ horse-shoes ” have each 
three to two rows of papillae ; on the hindermost there are sometimes only two rows or one. 
Most of the papillae had fallen off, and only some of the smaller ones were preserved; they 
were club-shaped, with a pointed upper end. The sides of the body are high in front, 
decreasing gradually behind. The double genital papilla is situated near the anterior 
end of the first (right hand) group of papillae. The foot is strong, broader in front, with 
a marginal furrow ; posteriorly it gradually decreases in size ; its free lateral margin is 
rather small ; the tail is provided with a strong dorsal keel. 
The intestines are visible through the body wall, especially on the back, less so at the 
sides of the body. 
The cerebro-pleural ganglia 1 are somewhat quadrangular in shape and flattened, 
united with each other by a short commissure behind the middle of the ganglion ; the 
line of division between the two component ganglia (cerebral and pleural) is very evident, 
the cerebral being a little the larger. The pedal ganglia are rather larger than the 
cerebral, somewhat compressed from before backwards, extending out from the infero- 
anterior portion of the underside of the former ganglia. The strong commissure is as long 
as the diameter of both cerebro-pleural ganglia ; not far from either end the commissure 
1 This agrees with the nomenclature used by Spengel in his excellent memoir, Ueber die Geruchsorgane und Nerven- 
system der Mollusken, Zeitschr.f. wiss. Zool., Bd. xxxv., 1881, p. 234. 
