104 
MR . E. C. BOUSFIELD ON THE 
corpuscles. First five segments destitute of dorsal setae ; the sixth 
and following having both dorsal and ventral setae, the latter 
hooked, the former straight, and one forked bristle in each bundle. 
Contractile loops in the sixth and some following segments, one 
in each. 
a. "Without secondary branchiae. 
1. Dero latissima, Bousjield (5). PL IV. fig. 8. 
Segments 30-40. Contractile loops 4. The branchial area 
with entire margin, well developed, width in full expansion 
exceeding length, capable of complete eversion, then becoming 
convex. Branchiae long, well developed, piano-cylindrical. 
2. Dero Perrieri, Bousjield. PI. IV. figs. 4-7. 
Dero obtusa, Berrier (22). 
Segments 25-35. Contractile loops 3-5. Branchial area with 
entire margin, trefoil-shaped in full expansion. Branchial pro- 
cesses well developed, cylindrical, the posterior pair longer than 
the anterior. 
3. Dero obtusa, D'TTdeJcem (6). PL III. figs. 1-3. 
Segments 45-50. Contractile loops usually 4 (4-6). The 
branchial area somewhat irregular, and apt to be unsymmetrical. 
Branchiae rather short, foliate ; the posterior margin nearly 
straight, the anterior curving outward at the middle. A dis- 
tinct dorsal lip, divided from the alar portions of the area by 
a deep groove on each side. 
This species shows the first trace of the modification which 
leads to the formation of supplementary branchial processes in 
the distinct demarcation of the dorsal lip, at the angles of which 
they are borne by those species which possess them. 
4. Dero Mulleri, sp. nov. Pl. IY. figs. 9, 10. 
Segments 70-95. Contractile loops usually 7 (6-S). The 
branchial area with separate dorsal lip. Branchial processes 
oblong, quadrangular, the attached border the longest, superior 
angles rounded. 
The largest of all known species. Furnished to the writer by 
Mr. Bolton. Chains of two zooids frequently consist of 130-140 
segments, and measure nearly an inch in length. Branchial area 
disproportionately small. 
