THE HETERONEEEIS PHASE OF A NEW SPECIES OF A 

 POLYCHAETOUS ANNELID FROM URUGUAY. 



By Aaron L. Treadwell, 



Of the Department of Zoology, Vassar College, Pougkkeepsie, New York. 



The following description is of the heteronereis phase of a new 

 species of Nereis sent me for identification by the United States 

 National Museum. The specimens were collected by the well-known 

 Uruguayan naturalist, Dr. F. Felippone, of Montevideo, in the course 

 of an expedition to the eastern coast of the Republic, oif Punta del 

 Este, Maldonado. He sa^'S : " The animal was not known to the 

 tailors. I captured it by placing an electric light (100 candlepower) 

 40 centimeters below the surface of the ocean. V/ithin five minutes 

 thousands of animals appeared on the water moving rapidly about." 

 Since paragnaths are found on all eight of the proboscis areas, the 

 species belongs in the subgenus Neanthes. The collection contained 

 only one male and a considerable number of females. 



NEREIS (NEANTHES) AUSTRALIS, new species. 



The single male was 37 mm. in length, with a width of 3 mm. in 

 the anterior unmodified portion. Females varied considerably in 

 size, depending in part on the degree of distension of the body 

 by the sex products. One female, the largest of the collection, was 

 95 mm. long and 6 mm. wide in the median region. 



The prostomium (fig. 1) narrows abruptl}^ at about the middle of 

 its length, so that it is roughly divided into two rectangular areas, 

 the outer one nearly square in outline, the inner one about twice as 

 long as wide. The eyes are prominent, those of the anterior pair 

 lying near the margin, while the posterior ones are at the postero- 

 lateral angles. The antennae are about one-half as long as the pros- 

 tomium, separated by less than their own width from one another. 

 The basal joints of the palps are large, extending to the apex of the 

 antennae, while the terminal joints are very small. The two ventral 

 tentacular cirri (only the anterior one is shown in the figure) are 

 short, hardly reaching to the apex of the prostomium. In the speci- 

 men drawn the anterior dorsal cirrus on the right side reached to 

 somite 8 while on the left it was much shorter, apparently due to in- 

 jury. The two posterior dorsal tentacular cirri extend to somite 10. 



No. 2499.— Proceedings U. S. National Museum, Vol. 64, Art. 9. 



1 



