JO Art. 5.— A. Izuka : 



Family T0M0PTERIDAE. 



Body elongate, thin; segments not numerous, without distinct 

 intersegmental constrictions. 



Parapodium long, cylindrical, provided ' with two broad and 

 soft fins which, in posterior parts of bodj^, are but very little or 

 scarcely at all developed. Setae and aciculum absent, 



Prostomium coalescent with peristomium, the former having 

 a pair of short tentacles, and the latter two pairs of tentacular cirri, 

 of which the second pair is very long and is supported each by a 

 long and very delicate bristle. Eyes two. Mouth ventral; 

 proboscis short, 



In this family there is only one genus, Tomopteris, known at 

 present. 



The body is very transparent; the alimentary canal is straight, 

 and the blood colourless. Eggs lie freely in the body-cavity. 

 Parapodia with or without " rosette-form " organs; fins with 

 fin-glands. The nerve cord, which is scarcely visible in living 

 specimens, is observed in alcoholic specimens to consist of two 

 lateral halves lying close together. 



Key to the species found in Japan. 



Rosette-form ' ' organs distinctly present in first 2 pairs of 



parapodia. Fin-glands and tail-region present 



Tomopteris pacifica, n. sp. 



'. "Rosette-form" organs absent. Fin-glands distinct. Fins 



occuring all around margin of parapodial rami. 

 b'. Both dorsal and ventral fins of 4th parapodium with fin- 

 gland T. elegaiis Chun. 



b". Ventral fin only of 4th parapodium with fin-gland. 



c. Fin-gland at tip of ventral ramus; first pair of tentacular 



cirri absent T. septentrionalis Qtfg. 



c". Fin-gland on ventral side of ventral ramus; parapodia in 



