134 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 92 
Genus POTAMETHUS Chamberlin 
POTAMETHUS MUCRONATUS (Moore) 
Ficure 15, a, h-j 
Notaulaz mucronata Moore, 1923, p. 248 (U.S.N.M. No. 17351; dredged off Santa 
Catalina Island, Calif., in 2,196 fathoms). 
There are several specimens in a mass of loosely intertwined, soft, 
mud-covered, slender tubes. The tentacular filaments are greatly 
elongated but of uneven lengths, and free for their entire length; 
they appear loosely attached to the thorax. There are no eye spots, 
stylodes, or color markings. The peristomial region is unusually 
prolonged, and the collar membrane does not nearly cover it. 
The setal formula of the thorax is: 
notopodia with bilimbate setae and spatulate setae (fig. 15, a) 
neuropodia with long handled avicular (fig. 15, h, 7) and pennoned setae (fig. 15, i) 
The pennoned setae are finer than the companion avicular setae, but 
the two have stems about equally long. They were seemingly over- 
looked in the original account since thoracic tori were said to have 
slender crotchets only. These fascicles are thus typical of the genus 
Potamethus. 
Only a few species have been attributed to this genus: (1) Potome- 
thus spathiferus (Ehlers) (1887, p. 278) originates from Florida, in 
275 fathoms; (2) Potamilla malmgreni Hansen, from Norway, was 
referred to it by Bush (1904, p. 208); (8) Potamethus scotiae 
(Pixell) (1913, p. 356) comes from the Antarctic. Another species, 
P. elongatus (Treadwell) (see below) comes from Hawaii. The first, 
second, and last appear to be distinguishable as follows: 
i. \Collar-membrane distinctly oblique? 222-20. ea ee 2 
Collar membrane straight except for ventral ends_______________ mucronatus 
2. Spatulate thoracic setae with a minute mucro_________________ spathiferus 
Spatulate thoracic setae with a long, pointed mucro (fig. 15, d@)____ elongatus 
POTAMETHUS ELONGATUS (Treadwell) 
FIGURE 15, b-d 
Potamilla elongata TreaDWELL, 1906, p. 1178 (U.S.N.M. No. 5221; Albatross 
station 3883). 
The type collection, labeled “Pailolu Channel, between Maiu and 
Molakai Islands, Albatross Sta. 3883, in 277 fms.,” contains frag- 
ments of a single individual and portions of a dark, fragile, slender, 
silt-covered tube, very weakly chitinized. There is part of an 
anterior end with some radioles still attached. These are long, 
slender, without eyes or stylodes; they are free for their entire 
Jength. Their attachment to the thoracic region is weak. The 
peristomial region is long, a considerable portion not covered by the 
