J. he few, hitliertu, Huffieiently known, genera of Linabricaluld', may 

 conveniently l>e arranged as follows: 



A. The efferent dnets partly grown together, at the base not 

 snrrounded by prostate glands. The efferent ducts and the Receptacle 

 open in the same porus. No atrinm, but heart. The dorsal vessel in 

 front threebranched. The ventral vessel not forked. — — 



Ocnerodrilus. 



B. The efferent ducts free, prostata present. The receptacle 

 (jpens in a separate porus. The dorsal vessel in front entire, the ventral 

 forked. Atrium, but no heart. 



I. The prostate glands surrounding atrium in all sides; the re- 

 ceptacle in front of the efferent ducts. 



1. All secondary vessels feathered, no exterior penis: 



Luiiibriciilns. 



2. Secondary vessels l)oth feathered and not feathered; no 



penis : 



Khyuehelinis. 



8. Secondary vessels ntit feathered; an exterior penis: 



Stjlodrilus. 



II. The prostate glands surrounding atrium only at the top; the 

 receptacle is behind the efferent ducts. 



4. The dorsal lateral vessels forked. One pair of receptacles: 



Phreatothrix. 



5. The dorsal lateral vessels not forked, but entire. Two 



pair of receptacles: 



Trichodrilus. 



As far as our present knowledge goes the following character- 

 istics will suftice fully to distinguish the above genera. 



Nova Acta Reg. Soc. Sc. Ups. Ser. III. 1 



