POLYCH ETA FROM THE N.E. PACIFIC. 957 
the rest. Hach neuropodium consists of a double ridge, with several 
rows of uneini. The dorsal surface is greatly flattened in the 
anterior region, and carries a median ciliated groove, which runs 
the whole length of the body in some forms, but is interrupted 
in others. 
Table of Genera. 
(a’) All segments behind anterior region similar. 
(6’) Notopodium of posterior segments unilobed 
(6) Notopodium of posterior segments bilobed 
(a’’) Median and posterior regions both present. 
(c’) Segments im median region with bilobed foliaceous 
notopodia, each carrying several capillary sete. 
(d’) Number of segments in median region variable 
(d’’) Two seements in median region ...... 
(c3) Segments. in median region typically with unilobed 
‘notopodia. Peristomial collar well dev eloped. 
(e’) Median segments two or three in number; noto- 
podia all conical in shape; tentacles long ...... Mesochetopterus. 
(e’’) Median segments five in number ; first with sepa- 
rate aliform notopodia; others with notopodia 
fused to form fans or suckers ; tentacles short... 
AS See eich Ranzania 
Telepsavus. 
Phyllochetopterus. 
Spiochetopterus. 
Chetopterus. 
MESOCHAETOPTERUS, gen. n. 
Chetopterids with a well-developed peristomial collar and « 
pair of long peristomial tentacles. Body divided into three 
regions. The anterior contains 9-13 setigerous segments ; th 
parapodia are represented by short and conical notopodia with 
capillary sete; in the fourth setigerous segment several of the 
dorsal setee are enlarged. The median region is composed of 
2 or 3 elongated segments, forming dorsally a flat region, with 
continuous lateral borders, covered with glandular epitheliwm 
and ornamented with transverse ridges. Typically the noto- 
podia are rather enlarged, conical, and fleshy, with a groove 
running down the inner border; the newropodia are single in 
the first, double in the succeeding segment or segments, and con- 
tain wuneint. The posterior region contains a large number of 
segments similar to those in Cheetopterus, but with much shorter 
notopodia. A dorsal ciliated groove runs from the mouth along 
the median line to the posterior end. In one or more of the 
median segments the lips are enlarged to form a fleshy organ. 
The genus thus agrees with Chetopterus in the reduced number 
and specialised character of the segments of the median region. 
It resembles Phyl/ochetopterus in the continuous ciliated groove 
and the long tentacles. 
Diagnoses of Species of Mesocheetopterus here described. 
M. taylori, sp.n.—A long but slender Mesochetopterus, living in 
a long narrow unbranched tube of opaque parchment, embedded for 
the most part vertically in sand and ending blindly. Prostomiwm 
very small, without eyes, entirely surrounded and hidden by the 
well-developed peristomial collar. The anterior region coniains 9 or 
