The prostomium (plate 3, fig. 3) is bilobed, though the depth of the median depression varies at different times during life. When fully expanded its anterior edge is nearly straight and it tapers on either side to a narrower base. The tentacles are longer than the prostomium, approximately equal in size, and only very gradually tapering to the apex. The green color noticeable in living material is lost on preservation, and it is then seen that a constriction occurs at each green band; this resembles an articulation, but I think is not a true jointing. There is one pair of small eyes.
The peristomium is rather short, though its absolute size naturally varies with the degree of expansion. The constriction between it and the second somite is very obscure, so that the two are practically continuous.
The gills begin as a single filament on the region of the twenty-fourth to the twenty-ninth somite and acquire a second filament a few somites behind this. They later have as many as 6 filaments (plate 3, fig. 4) and when fully developed meet from opposite sides across the dorsal surface. Posteriorly they become smaller and finally disappear entirely at about 45 somites from the posterior end.
The first parapodium (plate 3, fig. 5) with prominent dorsal and ventral cirri and a long, cirrus-shaped, posterior lobe. The anterior lobe is truncated. Two short, very black acicuke are in this parapodium and it carries dorsally a single tuft of needle seta. The ventral seta tuft is short and lies behind the ventral cirrus and contains compound and pectinate seta. The tenth pars podium has a large posterior lobe with the apex bent dorsally and a truncated anterior lobe. The ventral cirrus is conical, the dorsal with a decided lobe on its ventral surface. Three aciculse extend beyond the end of the pars podium. Parapodium 150 (plate 3, fig. 4) shows much less distinction be tween anterior and posterior margins than do the anterior ones. The ventral cirrus is small, borne on a rounded base, the dorsal cirrus also small with a ventral lobe. The gill is rather thick and heavy at the base, but soon divides into filaments. The seta are as in anterior somites and there are two aciculce.
In the body at the base of the gill is a black spot. Toward the posterior end the form of the parapodium changes very little, but the cirri become slender and a ventral light-brown acicula makes its appearance.
The simple setae are long, with a broadened terminal portion, but without noticeable fin or denticulations. The compound setae have very long terminal joints, not toothed at the edge (plate 3, fig. 6). This terminal joint is rela tively shorter through the gill region than anteriorly. Pectinate setae of two forms; anteriorly with 20 to 25 relatively very short teeth, the terminal ones not very long; through the middle of the body a second form appears, having not over 12 very prominent teeth (plate 3, fig. 7). These are more numerous than the other form in the region of the gills. The dorsal aciculle are black with rounded ends, the posterior ventral ones lighter in color and with a ter minal bifurcation.
The jaw apparatus is dark brown. The basal portion of the forceps is short and the median portion rather long, terminal portion gently curved, concave on inner surface. In larger individuals each inner paired plate has 4 teeth, though in immature specimens the proximal tooth may not appear. Outer paired plates with 7 teeth on the right side, 4 on the left, 2 of these being much larger than the others (plate 3, fig. 8). Unpaired plate with 6 teeth. Be yond these teeth the margin is usually smooth, but denticulations may appear in it. On either side beyond the toothed plates is a thin plate with its upper angle curved to form a tooth-like process. The mandibles have rounded shafts and are lighter in color than the maxillae, their apical beveled portion covered with a whitish deposit. (Plate 3, fig. 9.) Collected first at Mangrove Key in Key West Harbor in sand exposed at extreme low tide, in June 1915. It was fairly abundant in this locality and more were collected there in July of the same year. A single specimen was collected in the same season at Long Key, at the Dry Tortugas.
Type in American Museum of Natural History.