Taken in holdfasts of kelp, August 12, 1917.
In comparison with <i>N. tenuis</i> Moore, known from San Diego, this species differs in the form of the thorax, which is strongly angulate instead of terete the sides and venter being flat and the dorsum usually but little convex, so that the cross-section is nearly quadrate; also in having the segments and their subdivisions sharply separated with the posterior subsegment in each case much shorter than the anterior instead of equal to it. In the type the posterior thoracic somites are twice or more as long as wide, but in some paratypes the relative length is much less. Thorax narrowed caudad. The abdomen in its anterior part obviously thicker than the thorax in its widest part. The prostomium characteristic, showing two distinct regions, a broad posterior one with convex, anteriorly converging sides and a narrower, subconical, palpoidal terminal part sharply set off from the basal. Segments of abdomen irregularly multiannulate, sulci deep and surface usually appearing strongly rugose and uneven.
Length near 160 mm.; greatest width of abdomen, 1.4 mm.
Taken in sand and in growths of eel grass. The color is noted as reddish in life, as usual in the family.
Body with an anterior region of fifteen setigerous somites separated from a larger posterior region by a specialized somite, the sixteenth. Prostomium with a lateral process or horn on each side in front, notched in front at middle. Eyes none in genotype. Dorsal cirri present in addition to branchiæ on the first four setigerous somites. Notopodia with simple capillary setæ throughout. Anterior neuropodia with capillary setæ, but others also with crochets. Anal. cirri two.
Palpal processes lost from type. Proboscis as protruded short, distally expanded over proximal region. Parapodia dorsolateral in position, the anterior ones very thick. Principal postsetal lobe rising above into a branchial process which is short anteriorly but in posterior region is much longer, slender and subulate. Mesad of the branchial process of each parapodium of the first four pairs is a cirrus or cirriform process. The inferior setæ of the most anterior parapodia' much shorter than the dorsals, strongly curved. In the first notopodial fascia a much stouter, aciculiform, setæ which is uncate. Crochets with strongly narrowed neck; with two curved teeth at distal end above the beak which is decurved; in posterior region few in number, commonly four in a series. Anal cirri slender, filiform, much longer than the preceding branchiæ; one in the type has a short spur near its base. Total number of segments about one hundred and sixteen.