34 THE SHORTER SCIENTIFIC PAPERS 



not be recognized, although undoubtedly referable to the 

 genus Chaetogaster. 



The following table will serve to separate all the species 

 known at the present time: — 



A^. Prostomium distinct, usually with a pore on anterior margin 



C. dmtrophnis. 

 (Europe, N. America.) 

 A^, Prostomium indistinct. 



B^. Length of individuals not exceeding 5 mm. 

 C^. Esophagus as long as pharynx. 



D^. Blood vessels of pharyngeal region well developed C. langi. 



(Europe, N. America.) 

 D^. Blood vessels of pharyngeal region absent or only slightly 



developed C. crystallinus. 



(Europe.) 



C^. Esophagus shorter than pharynx, indistinct. 



D^. Ventral setae 8 to 12 in bundle, 1st postesophageal dila- 

 tion of intestine covered with anastomosing network of 



blood vessels C. limnoei. 



(Europe, N. America.) 



D". Ventral setae 6-7 in bundle, 1st postesophageal dilation 

 of intestine surrounded by 12 or more pairs of non- 

 anastomosing transverse blood vessels C. pellucidus. 



(N. America.) 



B^. Length of individuals 10-15 mm C. diaphanus. 



CHiETOGASTER LANGI Bretscher 



C. langi Bretscher, Kev. Suisse ZooL, vol. 3, p. 512, fig. 1, 1896; 

 Michaelsen, Das Tierreich, Oligocbaeta, Berlin, p. 21, 1900. 



Living specimens transparent. Prostomium blunt, in- 

 distinct. Setas unequally bifid at distal end, 4 in a bun- 

 dle. Esophagus long. Ventral ganglia glandular in 

 form. Circulatory system with normal development in 

 the pharyngeal region, 1 pair of transverse vessels (not 

 developed as "hearts") in esophageal segment. Length 

 1-2 mm. 



Between filaments of algae in swampy places, etc. 



One specimen referable to this species was obtained 

 early in July. There were several minor characteristics 

 not wholly in agreement with the description of C. langi. 



