250 bulletin: museum of comparative zoology. 



the arms of the oral disc having an elaborate system of circular and radial 

 muscle bands. 



Visceral Mass very small, relative to the size of the animal as a whole ; but 

 loosely held within the enormous atrial chamber. 



Branchial Sac situated within the visceral mass ; functionless as a respiratory 

 organ, but devoted to the nutritive function ; stigmata not numerous, irregular 

 in size, form, and distribution ; walls of sac without folds or internal vessels 

 or papillae ; dorsal lamina very short, in the form of two low ridges ; endostyle 

 likewise short and broad. 



Digestive Tract very short and broad, closely applied to the ventral side of 

 the branchial sac; liver and renal organ wanting. 



Gonads forming a compact mass closely applied to the posterior border of 

 the digestive tract. Ovary much larger, more or less cylindrical, situated im- 

 mediately behind the stomach ; apparently no oviduct. Testis placed at the 

 left end of the ovary, finely lobular, lighter in color than the ovary ; a short 

 sperm duct running forward on the ventral side of the intestine. 



Octacnemus herdmani. 



Octacnemus hythius Herdman, 1888, p. 88, and 1891, p. 648 ; Metcalf, 1900, 

 p. 572 ; and other authors, none of whom have examined the animals 

 themselves. 



Posterior, or Atrial end of the animal large and distinctly set off from the 

 anterior, disc-bearing end. 



Ventral Flange of the oral disc prominent, angular in section, and not con- 

 tinuous around the disc posteriorly, but each side running on to the atrial 

 portion of the animal, there to gradually disappear on each side of the attach- 

 ment patch, which is entirely behind the plane of the oral disc on the atrial part 

 of the body. 



Mantle of the Oral Disc not thickened in central portion, or otherwise struc- 

 turally set off for the other portions. 



Rectal portion of the intestine not projecting beyond the visceral mass ; anus 

 far forward. 



Distribution, eastern portion of South Pacific. 



In order to bring out clearly the contrast between this species and 0. bythius 

 Moseley, I subjoin a characterization of the latter species also. 



Posterior, or Atrial end of the animal much reduced, so that the attachment 

 patch is situated on the ventral side of the oral disc. 



Ventral Flange rounded, and continuous entirely around' the ventral side of 

 the oral disc ; hence not running on to the sides of the attachment patch. 



Mantle of the Oral Disc thickened in the central portion, this thickened part 

 octagonal in outline, the rays being the points at which the radial muscles are 

 inserted ; a small pit in the membrane in each interval between the rays, and 

 just beyond the thickened central area. 



