152 THP ANNELIDA POLYCHAETA. 



strongly flattened, foliaceous, and are attached to the surface of the somite 

 above and below the parapodia at or near the middle of their flat sm-face much 

 as mth true elytra. The cirri contain strongly developed and characteristic 

 glands which decrease in number caudad and which contain peculiar rod-like 

 bodies (possibly sensory nerve endings). 



Anal cirri two, commonly foliaceous. 



Alimentary canal presenting three divisions, pharynx, glandular stomach, 

 and intestine proper; above the anterior region of the alimentary tract lies a 

 highly characteristic diverticulum opening at the edge of the mouth, the so-called 

 "retort-formed organ" which is capable of protrusion either alone or in conjunc- 

 tion with the proboscis. 



Sexes separate. Development direct, without ciliated larval stages. 



This is an aberrant and small family of which but few species have been 

 recorded, these coming almost wholly heretofore from the Atlantic Ocean. 

 Reibisch (Ergebn. Atlant. Ocean * * * Plankton-exped., 1895, 2, H. c, p. 43-59) 

 lists six species. 



The Albatross collection from the Pacific represents five species of which 

 two are new and constitute a very interesting new genus noteworthy for the 

 remarkably developed nuchal organs. 



Key to Genera. 



a. With nineteen or more somites; head with a single pair of cirri. 



b. First free somite bearing dorsally a strongly developed pair of branchiform nuchal organs. 



Plotobia, gen. nov. 

 bb. First free somite with no such organs evident. 



c. Prostomium bearing a crown of flagella Typhlosculex Busch. 



cc. Prostomium without flagella. 



d. Tentacle abruptly set off from the prostomium; on the dorsal side of head a prominent 



bipartite lobe flanked on each side bj^ a ridge Trauisiopsis Levinsen. 



dd. Tentacle not abruptly set off, gradually widening into the prostomium, of which it appears 

 as a simple prolongation ; no such bipartite prominence on dorsal side of the prostomium. 



Sagitella Wagner. 

 aa. Somites sixteen; head with two pairs of foliaceous cirri Typhlodrilus Baldasseroni, 



Typhloscolex Busch. 



Beobach. anat. entwicke. wirbcllosen seethiere, 1851, p. 115; Reibisch, Ergebn. Atlant. Ocean*** 

 Plankton-exped., 1895, 2, H. c, p. 51. 



Typhloscolex mtjllerii Busch. 



Beobach anat. entwickl. wirbcllosen seethiere, 1851, p. 663; Reibisch, Ergebn. Atlant. Ocean * * * 



Plankton-exped., 1895, 2, H. c, p. 52. 

 Sagildla kowalewnkii form b, N. Wagner, Trav. Hoc. nat. St. Petcrsb., 1872, 3, p. 344. 



