258 ZOOLOGISCHE MEDEDEELTNGEN — DEEL IV. 



XIX. — ON A GIGANTIC NEREIS (NER. IJIMAI IZ.) FROM JAPAN. 

 BY Dr. R. HORST. 



Among the Polychaeta of the Leyden Museum I met with a large 

 iYgm's-specimen, presumably collected in Japan, that in the structure of 

 its parapodia so much agrees with Ner. ijimai x ) described by Izuka from 

 that country, that in my opinion it must be identified with this species, 

 though there are some discrepancies in the armature of the proboscis. 

 Nereis ijimai, like as Ner. oxypoda Marenz, Ner. virens Sars a. o. are 

 characterized by the presence of a large, foliaceous dorsal ligula at the 

 parapodia of the median body region and were ranged by Kinberg in 

 his genus Alitta 2 ). Unfortunately Izuka had only a single female spe- 

 cimen at his disposal, that was sexually mature and showed some 

 epitocous transformation after the 40th parapodium by the presence of 

 cultrate setae and epitocous lamellae; it had a length of 390 mm. and 

 consisted of 215 segments. Our specimen reaches 350 mm. and the number 

 of segments amounts to about 200; it is also a female, filled with small 

 eggs ; however it is not entirely mature and there are neither paddle- 

 shaped bristles nor epigamous lamellae. The proboscis was everted and 

 its armature consists of: 



I = a single indistinct paragnath (in Izuka's specimen absent). 

 II = a crescent, distichous group of 9 to 10 paragnaths (in 



Izuka's specimen in small groups). 

 IY = a crescent group of 16 to 18 paragnaths, the anterior ones 

 arranged in a single row (in Izuka's spec. 3 or 4 in a group). 

 Ill = a single paragnath (in Izuka's spec, absent). 

 Y = (in Izuka's spec, absent). 



YI = 8 to 10 paragnaths in a round group (in Izuka's spec. 6 

 or 7 pieces in an oblique group). 

 YII — YIII = a row of 7 rather large paragnaths, with traces of a second 

 row behind it (in Izuka's specimen a few large ones, with 

 minute ones scattered among them, in two continuous trans- 

 verse rows). 

 Taking into account the variability of the number of paragnaths in 

 the different groups of the proboscis in Ner. succinea Leuck. — diversi- 

 color O. F. Miill. a. o. I do not hesitate to identify the specimen óf the 

 Leyden Museum with Ner. ijimai Iz. 



1) The errantiate Polychaeta of Japan, p. 174, PI. II, fig. 1; PI. XIX, 



2) Annulata nova, p. 172. 



