BRITISH NEMERTEANS, AND SOME NEW BRITISH ANNELIDS. 425 



himself — that one may be allowed to have some doubt as to the correctness of pre- 

 vious descriptions with regard to the number of the bristle-bundles. The last of the 

 group is Trichobranchus glacialis, a species which Dr Malmgren has only described 

 from a spirit-preparation * This form was dredged in six to eight fathoms in Loch- 

 maddy, in 1865, as well as got under a stone amongst sandy mud at low water. 

 Length about f ths of an inch when moderately extended. Of a general blood-red 

 hue, or dark-red anteriorly, paler posteriorly. In shape the body is irregularly 

 fusiform, ending anteriorly in rich red lips, with a translucent projecting collar 

 at each side, leaving the dorsal and ventral edges free. From the dorsum, slightly 

 posterior to the fissure thus left, spring a tangled series of tentacles, which are 

 easily differentiated into three groups, even in the spirit-preparation. The most 

 conspicuous, long, thick cylindrical processes, varying from four to six in number, 

 arise distinctly behind the others, from the dorsal edge posterior to the cephalic frill, 

 and are distinguished by a bright-red central vessel, as well as by the frequency 

 with which they are thrown into spiral curves. They are capable of great exten- 

 sion, and seem more especially homologous with the branchia? of the Terebellse. 

 In front of the latter series is a dense mass of short, pale-pink, thread-like ten- 

 tacles, while a number of larger, clavated, red-streaked ones, arising from the 

 border of the lip, are in the centre of these. The latter become grooved in con- 

 traction. In fine specimens, the varying habit of these three groups of tentacles 

 is very marked. Four annulations occurred on the ventral, and three on the 

 dorsal aspect (the first not being visible after immersion in spirit), before the 

 bristles appeared. These are ranged on fifteen prominent papillae, and during 

 life are frequently directed forwards. The arrangement of the bristles in the 

 fascicles is peculiar, for they are grouped in pairs — a large and small one alter- 

 nately — to the number of six (twelve bristles). The latter (Plate XVI. fig. 8) 

 are proportionally strong, and taper from a little above the base to a slightly 

 bent apex. For about a third of the distal portion, there is a very narrow wing 

 or border at each side, which has minute striae directed forwards and outwards. 

 A row of hooks runs in a transverse manner on the ventral surface from each 

 bristle-papilla, the anterior rows being closer to the papilla than the posterior. 

 These hooks (Plate XVI. figs. 6 and 7) have an elongated and slightly-curved 

 form like those of Terebellides, the head possessing a strong beak, behind which 

 are a series of small processes or fangs. There is a distinct narrowing or neck 

 below the head, and the hook gradually tapers from the succeeding shoulder 

 backwards. This form of hook is confined to the somewhat prominent pads of 

 the bristle-bearing segments. A series of elevated mamillse succeed the latter, 

 each being furnished with a row of short hooks, which differ entirely from the 

 foregoing (Plate XVI. fig. 7 a). Each has a short and wide basal process, a 



* Nord. Hafs-Annulat. p. 395, tab. xxiv. fig. 65. 

 VOL. XXV. PART II. 5 Q 



