20 Journal of Entomology and Zoology 
narrowly bilimbate, drawn out into a very fine simple tip. Uncini, at least for the most 
part, in two series both in thoracic and in abdominal region; apparently with mostly 
three transverse rows of denticles at vertex; beak long, the sinus with parallel sides, 
opposite side of body evenly curved, not distinctly shouldered. Total number of seg- 
ments in the type, which is complete, about one hundred and thirty, of which II to 
XXVII are setigerous. Body rapidly narrowed to the eighteenth segment, but only 
very gradually thereafter. 
Length, near 45 mm.; greatest width, 1.8 mm. 
Type—M. C. Z. 2, 169. 
Balboa. 
SABELLID-E 
Myxicola monacis sp. nov. 
In size and general appearance resembling M. pacifica Johnson, with the type 
of which it has been compared. From that form the present one may readily be dis- 
tinguished in having the ventral median prccess from the first segment drawn out into 
a slender entire tip instead of being broad and presenting distally two angles or 
lobes; the process is furrowed longitudinally and the edges are somewhat turned 
down. Branchie twenty-two pairs. Readily distinguished by the form of the abdominal 
uncini. These have the general form of those of pacifica but as a whole are longer 
with the body proportionately more slender and its abvertigial end more rounded; the 
beak is longer and less divergent, distally curving a little back toward the body; the 
sides of the sinus parallel. The body in the type is somewhat fusiform, being nar- 
rowed both ways from the middle but more strongly so caudad. In a paratype the 
body is scarcely narrowed cephalad. Body scmewhat depressed dorsoventrally, less 
terete than in pacifica. Total number of segments near seventy. 
Length of type, exclusive of branchiz, 40 mm.; greatest width, 6.2 mm. 
Type—M. C. Z. 2, 170. 
Taken from holdfasts of seaweeds. 
Potamilla clara sp. nov. 
The body in general light brown; but ventrally there is a median longitudinal 
fulvous stripe over the ventral plates. The branchie are crossed by a series of dark 
bands or annuli which fade out proximally, about three distad of the middle of length 
being deep and distinct. There are nineteen pairs of branchial radioles; barbs nu- 
merous, densely arranged to near tip, the naked distal region of axis very short, pale 
excepting where partially or completely involved by the transverse dark bands. Ven- 
tral lobes of collar moderate, rounded, edges a little rolled down; dorsal ends separ- 
ated; no lateral incisions, being but two-lobed; not produced forward below, lobes 
rounded and separated. Thoracic segments eight. Ventral plates all rectangular, 
those of the abdomen divided by the midventral sulcus. Total number of segments, 
sixty. 
Length without branchie 21 mm.; length with branchie, 28 mm.; greatest width, 
3 mm. 
Type—M. C. Z. 2, 171. 
Taken on beach at low tide. 
Potamilla omissa sp. nov. 
The general color is dusky or pale brownish with the anterior ventral plates 
lighter and the branchiw rather weakly transversely banded with dark. Radioles of 
