384 HALOSYDNA GELATINOSA. 



at the ventral edge, with short spinous regions having a marked dorsal curve, presenting 

 only a short knob, smoothly rounded, at the tip (Plate XL, fig. 30). 



The dorsal cirri are stout, shorter than in M. castanea, brownish, and, in spirit, taper 

 from base to tip, a few short clavate cilia occurring on the surface. The ventral cirri 

 are slender and tapering, and only reach a little beyond the bases of the nearest bristles. 

 A few short clavate cilia are present. 



Habits. — This species is probably commensalistic on another form, probably an 

 echinoderm, but hitherto it has occurred at St. Andrews only in the free condition, viz. 

 as thrown on the beach after storms. 



n i 



Genus XIX. — Halosydna, Kinberg, 1857. 



Body linear-oblong ; head continuous anteriorly with the bases of the median and 

 lateral tentacles. Eyes large. Palpi smooth. Xuchal collar with a prominent flap. 

 Segmental eminences distinct and the papillae long. Proboscis with twenty-two frilled 

 papillae along each border. Only two short, wide, and glandular gastric caeca pass 

 forwards into the peripharyngeal space. Scales eighteen pairs, large, soft, and with a 

 frilled outer border, not covering the dorsum. Dorsal division of the foot minute, with 

 slender, simple, and finely spinous bristles. Ventral division rather long, with numerous 

 somewhat slender bristles with tips of varying breadths. 



Halosydna gelatinosa, M. Sars i 1860. Plate XXV, fig. 5. 



Specific Characters. — Head ovoid, pinkish, running into the bases of the lateral 

 tentacles. Transverse diameter greatest. Eyes large, furnished with lenses, close 

 together, the larger anterior pair on the lateral prominence, and the posterior close 

 behind. The median tentacle is long, smooth, and tapering, with a filiform tip, and the 

 lateral tentacles are also long. The tentacular cirri agree with the median tentacle in 

 length and structure. The palpi are of moderate length, and smooth. Most of these 

 organs are tinted pale madder-brown. Body elongated, bristled segments forty- 

 three, barred transversely with pale greyish-brown belts between the pedicles for 

 the scales. The nuchal collar has a prominent flap, which covers the posterior part of 

 the head. Segmental eminence distinct, and the papilla long. The proboscis is charac- 

 terised by about twenty-two frilled papillae along each border in extrusion, and a 

 muscular fold at each side. Scales eighteen pairs, not covering the dorsum completely, 

 large, soft, and rounded, with a folded or frilled outer border in spirit. The outer region 

 is studded with minute trifid papillae, but the margin is quite smooth throughout. The 

 dorsal division of the foot is minute, with slender simple and finely spinous bristles. The 



1 Kinberg, in his description of the genus, gives little to discriminate it from Lepidonotus except 

 the numerous elytra and the elongated body. 



