Length of type, 21 mm.; greatest width, 2.2 mm.
The type of this species is in the epitkous phase. The middle region of the body bears notopodeal fasciæ of long, fine, simple, natatory setae in addition to the compound neuropodials. The appendage of the compound setae differs from that of _californiensis_ in having the accessory tooth farther distad, well beyond the middle of the concave edge, whereas in the other species it is normally rather proximad of the middle. In the present species the prostomium is proportionately larger, less covered by the peristomial flap which does not extend over the base of the median tentacle. The palpi are not fused so far distad, being united only at base; they present below on each a large distal lobe similar to that in the other species. Eyes with prominent lenses; large; those on each side sub-contiguous. Median tentacle in line with the centers of the anterior eyes; short and pointed, shorter than the width of the prostomium. Paired tentacles a little shorter than the median; each attached in front of the median at a point midway between the latter and the anterior eye. Tentacular cirri much longer than the tentacles, attenuated distad, pointed. The notocirri are all similarly attenuated and run out to a rather fine point. Neurocirri very thick, conical, each with a black dot near middle. Contrasting with the preceding species in color in having the dorsum in general light, fulvous, in part slightly dusky, with a series of dark, blackish, transverse lines across dorsum, there being four somites between each two dark lines. The body is narrowed toward both ends; venter flat and dorsum strongly arched; hesioniform. Because of the broken condition of the type the number of segments is uncertain, but is near seventy-five.
Greatest width, exclusive of parapodia, 1.5 mm.
Like _Streptosyllis_ in having the pharynx strongly sinuous and unarmed and in lacking nuchal flaps such as characterize _Amblyosyllis_. It differs from the former genus in having only composite setae and in having these of the ordinary structure, the appendage of a simple, fringed form not covered by a membrane. Eyes two pairs instead of three. Tentacular cirri two pairs. These, as also the tentacles and notocirri, short, articulated. Neurocirri attached proximally.