18 THE VOYAGE OF H.M.S. CHALLENGER. 



the right. The lateral plates (figs. 5, b, b, 6) agreed with those of the typical form, exhibiting 

 on the posterior (superior) cutting edge of the hook almost always about 12 comparatively 

 fine denticles, and on the anterior (inferior) edge 4 very strongly developed. 



The oesophagus did not differ from that of the other Marsenice, it was posteriorly 

 enlarged, and exhibited far back the usual somewhat long saccular dilatation. The foli- 

 ated or glandular stomach had a yellowish colour, and a cap-like shape due to the con- 

 cavity of the anterior surface ; the stomach-cavity was as usual small, and the thick wall 

 exhibited the normal foliated structure of a glandular character. This stomach was 

 covered by the usual rather thick glandular layer. The slightly ascending pyloric tube 

 opened into the true stomach, which lay along the right side of the posterior wall 

 of the superior visceral mass. Near the pyloric opening was that of the bile-duct. 

 The stomach was continued on the left into the intestine, which was throughout the greater 

 part of its course filled with white, round or oval excrement balls. It was continued 

 along the anterior surface of the liver, and further forwards (fig. 2). The contents of 

 the digestive cavity were unrecognisable animal fragments. The liver was yellowish 

 white, and in other respects as in other Marsenice. 



The pericardium and the heart, the kidney and the foliated gland, exhibited the usual 

 structure and relations (fig. 2). 



The faintly yellow testis was destitute of ripe gonoblasts. The vas deferens formed 

 the usual twisted ball, and extended forwards in a straight, and afterwards in a coiled 

 course, first within the body- wall, and then free to the penis. The latter (fig. 3, a) 

 exhibited terminally an unusually marked protrusion (fig. 3, b) of the vas deferens. 



This form of Marsenia, though somewhat doubtful, seems to differ from the Mediter- 

 ranean species, though it is perhaps only a local variety. 



Marseniopsis, n. gen. 



The Marseniopsides differ strikingly from the other Marseniad genera. They form a 

 beautiful transition-link between the diclinous and the androgynous (Marsenina, Onchi- 

 diopsis) Marseniadse, and distinctly demonstrate a unity of relationship which makes it 

 impossible to split up the family. In their general form they agree with the Onchidi- 

 opsides ; the superior part of the body is hemispherical, as if distended; the mantle 

 margin is thick and swollen ; the external mouth lies far forwards. They have, however, 

 no right exhalent fold nor associated semi-canal, and the branchial folia rather resemble 

 those of the Marsenia. The mandibular plates are narrower, and, on the whole, smaller, 

 than in other Marseniadse. The lingual armature, on the other hand, agrees exactly with 

 that of the androgynous forms ; outside the lateral teeth there are, in addition, two hooked 

 plates. The Marseniopsides have the sexes separate. The anatomical relations resemble 

 most closely those of the Chelyonoti ; the inferior portion of the vas deferens does not lie 



