NEMATONEBEIS UNICORNIS. 453 



Genus LXXIL— Nematonerims, Schmarda, 1861. 



Head smoothly rounded, with a single median tentacle. Body elongated and 

 distinctly segmented ; two segments devoid of feet. Upper dental apparatus with an 

 uneven number of plates. The body- wall of Nematonereis unicornis is thick and muscular, 

 after the type of the Eunicicla3 and Lumbriconereidse. The nerve-area is pyriform with 

 the narrow end inferiorly — as a short pedicle. The area has a thick coating of cells which 

 stain deeply. A small neural canal exists in the centre superiorly. The oblique muscles 

 are attached to the upper and outer border, and some fibres pass down to the apex of the 

 nerve-area. The hypoderm forms a thicker layer in the centre inferiorly, and the fibres 

 of the circular coat curve inward along its inner border and apparently cross below the 

 nerve-area. On the inner aspect of the area in certain parts is a coarsely granular 

 brownish layer which does not stain well, and is probably fatty. Foot with dorsal and 

 ventral cirri; simple bristles, with a few brush-shaped forms, dorsally; jointed hooks 

 inferiorly. 



Ehlers (1868), characterizes the genus as having a single tentacle ; two segments 

 devoid of feet. Foot with dorsal and ventral cirri, simple and compound bristles. 

 Upper jaws with an uneven number of jaw- plates. 



1. Nematonereis unicornis, Grube, 1840. Plate L1V, fig. 3; Plate LXIII, figs. 5 and 

 ha— teeth; Plate LXXV, figs. 3 and 3 a— feet ; Plate LXXXIV, figs. 1-1 c— 

 bristles. 



Specific Characters. — Head smoothly rounded in front ; two large black eyes at its 

 posterior border and between them a subulate median tentacle. Body five to six inches 

 long, pale pinkish and iridescent in front, posteriorly cream-coloured with a pale 

 orange streak from the intestine. The anterior of the first two segments is the broader. 

 The body terminates posteriorly in four (Ehlers) anal cirri. Maxillse short and 

 strongly hooked anteriorly, their posterior appendages of an elongated conical outline. 

 Anterior plates have a triangular brown patch in front. Great dental plates have four 

 or five large teeth. 1 Mandibles hatchet-like, the expanded anterior blade with parallel 

 lines. The vascular anterior feet {e.g., tenth) have a subulate dorsal cirrus. The 

 setigerous region has a single brown spine ; above it two groups of winged bristles with 

 attenuate tips. Below the spine are jointed hooks which have the dilated end of the 

 shaft minutely serrate. Ventral cirrus pear-shaped. Behind the foregoing the dorsal 

 cirrus by-and-by becomes more slender and has a distinct granular enlargement at its 

 base. A single group of winged bristles with attenuate tips and a few brush-shaped 

 forms occur above the spine, whilst the jointed bristles beneath are stronger. The whole 

 setigerous region is proportionally less, but it is more prominent. A single powerful 

 hook projects above the ventral cirrus from the twentieth foot backward. 



Synonyms. 

 1840. Lumbriconereis unicornis, Grube. Actin. Ecliin. u. Wiirm., p. 80. 



1843. „ pectinifera, De Quatrefages. Mag. de Zool., 2 e ser., y, p. 6, pi. ii, f: 3 — 8. 



1861. Nematonereis unicornis, Schmarda. Neue Wirb. Thiere, ii, p. 119, pi. xxxii, f. 254. 



1 Unfortunately the only example available for illustration was injured (Plate LXIII, fig. 5). 



