MYSTIDES BOREALIS. 433 
as swimming-bristles. Gravier, however, found females with much developed eggs in which 
these bristles were disappearing. 
MystIDEs (PROTOMYSTIDES) BIDENTATA, Langerhans, 1880. Plate CX XXIV, fig. 10—bristle. 
Specific Characters—Head somewhat elongate, tentacular cirri rather long. Body 
5—25 mm. in length. Segments 190. Colour greenish-yellow, and the segments are well 
marked. A dark brown pigment-spot occurs ventrally at the base of each foot. Anal 
seoment with two slender cirri, enlarged at the base, and tapering distally, a long papilla 
between them. Feet with ovate cirri; setigerous lobe bifid. Ventral bristles thicker than 
the median, and the terminal pieces shorter; dorsal bristles intermediate. The dilated 
and bevelled tip of the shaft bears two unequal claws, and is spinous. On the whole the 
bristles are longer and more slender than in M. lumbata. The ventral cirri of the second 
seoment are large. Mature male with swimming-bristles in June on segments 40—157. 
Female has greenish ova, and swimming-bristles from the sixty-sixth segment. 
SYNONYMS. 
1880. Mystides bidentata, Langerhans. Zeitschr. f. wiss. Zool., Bd. xxxui, p. 310, pl. xvii, fig. 46. 
1888. a %, De St. Joseph. Ann. Se. nat., 7° sér., t. v, p. 308, pl. xin, figs. 1883—185. 
1914. 3 (Protomystides) bidentata, Southern. Proc. Roy. Irish Acad., vol. xxxi, No. 47, p. 71, 
pl. vin, figs. 17 a, B. 
1921. : limbata, McIntosh. Ann. Nat. Hist., ser. 9, vol. vii, p. 297. 
Habitat.—Dredged in 24 fathoms, Clew Bay, and in 16 fathoms near Bofin Harbour 
(Southern). . 
Shores of France (De St. Joseph) ; Madeira (Langerhans) ; Mediterranean. 
The head is elongate, and the tentacular cirri long. The body has about 190 segments, 
and measures from 5—25 mm., the colour being greenish-yellow, and a dark brown spot 
exists at the base of each foot ventrally. The anal segment has two slender cirri enlarged 
at the base, and a long papilla between them. The feet have ovate cirri, and the setigerous 
lobe is bifid. The ventral bristles are thicker than the median, and the terminal pieces 
shorter; dorsal bristles intermediate. The dilated and bevelled tip of the shaft bears two 
unequal claws, and is spinous (Plate CX XXIV, fig. 10). The bristles are longer and more 
slender than in M. limbata, and the ventral cirri of the second segment are large. Mature 
forms have swimmineg-bristles. In contrast with M. limbata, the coloration of this species 
differs, and the dorsal and ventral cirri appear to be proportionally larger. 
MystIpDEs BOREALIS, Théel, 1878. Plate CX XXIV, fig. 11—bristle. 
Specific Characters—Head rounded in front, broader behind, and has four long, slender 
tentacles. No eyes in some. Nuchal grooves between the head and first segment, which 
bears a single pair of tentacular cirri. ‘Two pairs of tentacular cirri on the second segment, 
the dorsal being the larger, and all have a basal articulation and a swelling above it. Body 
54 mm. in length, and has thirty-eight or more segments. Colour greenish-yellow in 
