's RIJKS MUSEUM VAN NATUURLIJKE HISTORIE — LEIDEN. 445 



totally disappeared and in both foot-lobes only a stout, black acicula is 

 present, whereas the dorsal cirrus is strongly developed and extends a 

 good deal beyond the extremity of the dorsal ligule. The anal opening 

 is surrounded by a circle of papillae. In the females the epitocous trans- 

 formation of the feet ceases with the 75 th to 85 th segment; the swimming 

 bristles have disappeared and instead of them the ordinary setigerous 

 setae are to be seen. 



According to the armature of the proboscis this species ought to be 

 ranged among the subgenus Neanthes and is closely allied to Nereis 

 cricognatha Ehl. ] ) and N. caudata Dch. 2 ), which both have group I 

 composed of several paragnaths and have the lobes of the parapodium 

 provided with an elongated conical anterior lip. Both species however 

 are distinguished from N. notihuysi by having all the paragnaths of the 

 oral region of the proboscis united in a single coherent girdle. 



It is a remarquable fact, that Nereis nouhuyn, though living in fresh- 

 water, acquires the Heter •oner 'm-form, when attaining sexual maturity; 

 for other euryhaline species of this genus, like N. limnicola from lake 

 Merced (California) according to the observations of Johnson 3 ), and N. 

 cliversicolor, as demonstrated by Mc Intosh, breed in the atokous state. 

 Gravier however has described Perinereis seurati 4 ) from a fresh-water 

 pond in Tarauru-roa (Gambir isles), which showed some traces of a 

 Heter •oner eis-state, consisting of two foliaceous bobes at the neuropodium 

 and at the ventral cirrus, whereas the dorsal part of the parapodium 

 remains unchanged and swimming bristles do not appear. 



1) Ehlers, Neuseelâudische Anneliden, I, Abhand. K. Gesellsch. Wissensch. Göttingen, (N. F.) 

 Vol. Ill, 1904, p. 29, PL IV, figs. 3—7. 



Augener, Fauna Siidwest-Australiens, Polychaeta errantia, 1913, p. 163. 



2) Claparède, Armel, chétopodes du Golfe de Naples, p. 478, PI. X, fig. 1, PI. XT, fig. 3. 



3) Fresh-water Nereids from the Pacific coast etc.; Mark Anniversary Volume, 1903, p. 208, 

 PI. XVI, figs. 1—10. 



4) Bulletin Muséum d'Hist. naturelle, Vol. XI, 1905, p. 243. This species afterward was also 

 met with by Dr. Merton in the Waskai river; Ehlers, Polych. Anneliden von den Am- und 

 Kei-Inseln, p. 239. 



