266 Papers from the Department of Marine Biology. 



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 seta? are long, with a broadened terminal portion, but without 

 noticeable fin or denticulations. The compound seta? 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 aciculae 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 maxilla?, 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. 



FAMILY SABELLID^I. 



Sabella alba n. sp. 



Length 45 mm., of which the gills represent 10 mm. Body very slender, 

 not more than 2 mm. in breadth at the collar. 



Gills 17 pairs, colorless except for a fine longitudinal dusting of pigment 

 along the bases of some of the rachises ; bases of rachises connected by a very 

 delicate membrane. On the outer surface of the rachises beyond the edge of 

 the membrane are minute black ocelli, of varying number on different rachises 

 and on different sides of the same rachis. These seem never to be more than 12 

 in a row. The extreme tip of each rachis is free from pinnules. The antennae 

 are slender, sharp-pointed, with (in alcoholic material at least) a noticeable 

 white longitudinal median line. On either side, ventrally, is a patch of fine 

 dark-brown spots similar to those found on the bases of some rachises. 



The collar is rather low, its ends widely separated dorsally, but nearly in 

 contact on the ventral surface (plate 3, figs. 10 and 11). The ventral ends 

 have a fine recurved tip, but elsewhere the edge is straight and not recurved. 

 On either side is a ventro-lateral fissure, giving the collar a 4-lobed character. 



Body colorless except for a series of dark-brown ventral shields on the 

 somites. Throughout the greater part of its length these shields are divided 

 by a deep, narrow longitudinal fissure. There are 8 thoracic somites. 



Thoracic seta? of two sorts, one (plate 3, fig. 12) lanceolate with asymmetrical 

 expansion at the end, the other stouter, enlarged at the apex, shown in side 

 view in plate 3, figure 13, and in full face in figure 14. The setae of the collar 

 fascicle are lanceolate like those shown in figure 12. Uncinus of thorax with 

 a single tooth and a definite crest of minute denticulations, but without second- 





