482 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 99 



the innermost muscle layer for most of their length and are not in 

 the form of a dissepiment at right angles to body wall. 



Nephridia two, small, the lips of nephrostome greatly prolonged 

 but not in a spiral. Nephridiopores are rather close behind the setae, 

 but farther from nerve cord than setae. 



The foregut survived only in the type. It is fairly long, with a 

 well-marked gizzard, the anterior end of which coincides with the 

 posterior margin of the double ventral mesentery. In front is the 

 esophagus, thrown into loops and held in place by the ventral mesen- 

 teries, while the short pharynx is attached to body wall by numerous 

 radiating muscular frenula. The stomach is more inflated than giz- 

 zard, and its translucent walls are marked by longitudinal lines. A 

 a very short distance posterior to attachment of neurointestinal vessel 

 a very inconspicuous ciliated groove begins, but the length of presi- 

 phonal intestine can not be determined. In one specimen are two 

 fragments of the intestine having a well-developed siphon. 



The vascular system is characterized by absence of any relation 

 with the interbasal muscle of setae, and the absence of a direct well- 

 marked ring vessel. Near the intestine the neurointestinal vessel 

 divides in two, and where it meets the wall at posterior end of stomach 

 there is a slight inflation. But beyond this point there is no simple 

 vessel passing over the wall to join the dorsal blood vessel, the in- 

 flated part of which ends at middle of stomach, to be continued a 

 short distance by a very constricted vessel. There seems to be no 

 alternative but a nexus through numerous small vessels in the wall 

 of stomach, a very unusual condition outside the Bonelliidae (except 

 in Arhynchite) . 



Type.—V.S.'^M. No. 21082. 



Type locality. — Albatross station 4547, 10.5 miles northwest of Point 

 Pinos, Monterey Bay, Calif., 1,083 fathoms, gray mud, rocks, June 6, 

 1904, 4 specimens. Near this locality, at station 4537, 1,041 fathoms, 

 the bottom temperature was 38.5° F. 



Genus LISTRIOLOBUS W. Fischer 



Listriolo'bus W. Fischer, 1926, p. 110 (type, Listriolobus bahamensis Fischer). — 

 FisHEB, 1946, p. 233. 



Diagnosis. — Differing from Thalassema s. s. in having elongate, 

 spirally coiled lips to nephrostome and 6 to 16 (type) narrow meridi- 

 onal thickenings of the middle longitudinal muscle layer. Differing 

 from Anelassorhynchus in having these same muscle bands, and from 

 Ochetostoma in having the inner oblique layer a smooth continuous 

 sheet not divided between the muscle bands into separate fascicles. 

 Nephridia one to three pairs; interbasal muscle of setae present or 

 absent. 



