DESCRIPTIONS OF GENERA AND SPECIES 289 



The latter give off a similar branch which, before uniting with the perioesophageal 

 of the fifth segment, is connected twice with the lateral vessel of its side. The 

 perioesophageal vessel of the fifth segment gives off a branch which joins that 

 of the sixth ; the latter bifurcates, and has two separate unions with the ventral vessel. 

 This is an approach to the irregular network of N. josinae. There are slight variations 

 in the setae, sometimes two uncinate or no capillifonn in the dorsal bundles, but 

 the above is the normal arrangement. The pigmented covering of the intestine begins 

 in the sixth segment. 



(10) Nais reckei, FLOERICKE. 

 Ophidonais reckei, FLOEBICKE, Zool. Anz. 1892, p. 469. 



Definition. liorsal setae short, straight, and pointed. Other characters as in N. serpentinn. 

 Jfab. Germany. 



The setae of this species are unlike those of any other Naid. They are straight and 

 cylindrical, and suddenly end in a fine point. 



Genus PRISTINA, EHRENBERG. 



Syn. Pristina, EHRENBERG. 

 Pristinais, GERVAIS. 

 Nais, D'UDEKEM (in part.). 

 Stylaria, TAUBER (in part.). 

 Naidium, SCHMIDT. 



DEFINITION. Dorsal setae commence in the second segment, capillary only or 

 capillary and hastiform, the latter bifurcate or not bifurcate at extremity. 

 Eyes absent. Glandular ventricle present. Septal glands well developed. 



I venture to differ from all recent authorities, in combining the two genera 

 Pristina and Naidium. This step appears to me to be rendered necessary by 

 BOURNE'S (5) description of two species which nearly entirely bridge over the gap 

 which formerly separated the two genera. Previous to the publication of that paper 

 the two genera might be thus distinguished. 



PRISTINA. NAIDIUM. 



(1) Dorsal setae of segment iii very long. (i) These setae not longer than the others. 



(2) No bifid hastiform setae in dorsal (2) Such setae present in dorsal bundles. 



bundles. 



(3) Prostomium elongate. (3) Prostomiuin short. 



Pp 



