EEPOET ON THE ANNELIDA. 
143 
structure, and its surface and margins are smooth. The second scale is about the same 
size, but has along its outer border five or six digitate processes, some of the stems being 
undivided, others bifid or trifid. The scales greatly increase in size after the third, and 
their outer margins are furnished with well-marked processes. In shape they are 
irregularly quadrate with a straight outer (or inferior) margin, along which the charac- 
teristic papillae are ranged (PI. XXV. fig. 3). The papillae are in a single row, and 
commence at the anterior angle in the form of a process or two with the- tip split into 
three long divisions or digits ; then the latter in the succeeding reach four or five, and 
toward the posterior border again diminish to three, and finally end in a simple filiform 
process. In minute structure (PI. XXIII. fig. 1 2) the exterior of the entire process is 
covered with transparent cuticle, which is dense on the main stem and thinner on the 
divisions, especially towards the tip. It rests on a granular portion of the scale, 
and the same hypodermic structure is continued into the centre of the process, an 
enlarged region occurring at the base of the divisions. In the latter the granules are 
finer and more translucent, indeed, they gradually become indistinct toward the tip. 
The posterior scales are reniform, and the digitate processes occasionally show a maximum 
of six or seven divisions. The nerves from the scar of attachment (umbilicus) are 
distributed to the papillae in a very suggestive manner. It would appear that in some 
cases at least the scales in Sigalionidae are even more diagnostic than the bristles. 
When fully formed (in the anterior third of the body) the foot has superiorly a 
branchial process, two ciliated cups on the dorsum, and a process in the inner angle 
under the branchia. The dorsal division bears the usual serrated (whorled) bristles, 
which are more evidently pinnate in some than in others. There appears to be a 
d iffi culty in regard to the specific differences to be found in such bristles, and at the 
present moment no stable distinctive character can be adduced. Thus the thick part 
of one of the dorsal bristles of this species (PI. XIIIa. fig. 11) diverges very little from 
that formerly shown in Thalenessa digitata. 
The ventral division of the foot bears a group of the usual bifid bristles, the upper 
and lower series having longer tips than the central, some of the lower indeed in the 
anterior third of the body showing two segments in the terminal portion. The middle 
series, like the foregoing, present a few spinous rows below the tip of the shaft 
(PL XIIIa. fig. 12), and the terminal bifid piece is moderately elongated. 
The ventral cirrus is somewhat long, and its slightly bulbous tip extends con- 
siderably beyond the setigerous lobe. There are several small papillae in front of and 
behind the pedicles for the scales, and one on the ventral margin of the foot to the inner 
side of the cirrus. The ventral papilla occurs in the fissure behind each foot, and its 
basal enlargement presents a fold or pit externally. 
The structure of the body-wall in this form corresponds in the main with that in 
the previous species. The transverse band over the nerves is perhaps more distinct as 
