266 ME. E. C. BOUSriELD ON 



like the serrated margin shown in Yejdovsky's figure, reproduced 

 in the drawing (fig. 3). As a rule, there is one ring round each 

 of the first four bristle-beariug segments and two round each of 

 the following, the one corresponding (as in the first form) with 

 the position of the setse, the second round the middle of the 

 segment. The tail, like the head, is provided with a greater 

 number somewhat irregularly disposed. These organs are usually 

 wanting on the under surface, and each ring is composed of from 

 six to eight. 



The eyes are purple ; the corpuscles of the perivisceral fiuid 

 oval, hyaline, showing no trace of granules, and very abundant. 



These characters will, I think, suf&ce for the identification of 

 the species ; I pass, therefore, to show the diiferences between 

 it and the Nais appendiculata of D'TJdekem, to include which 

 the genus Slavina was founded. 



In this species the first pair of bristle-bundles on the dorsal 

 aspect consist of two or three long fine bristles in each, with one 

 or two shorter ones, so that there may be as many as from three 

 to five in each ; whilst the succeeding bundles each contain two or 

 more short bristles, not exceeding in length the transverse dia- 

 meter of their possessor, or but little exceeding it, being, accor- 

 ding to Yejdovsky's account, so fine that it might be thought 

 almost that they were absent. 



The touch-organs are arranged in a single row round each 

 segment, are much more numerous, as many as twenty in each 

 ring, and are found on the under surface as well. 



The eyes are brownish black ; the number of segments and the 

 character of the corpuscles of the perivisceral fluid are similar to 

 those of the Nais lurida of Timm. 



Whilst engaged in studying the characters of these worms, I 

 received from Mr. Bolton several specimens of a worm which I 

 was at first inclined to regard as a new species, which also 

 possessed the touch-organs already described; but on further 

 consideration I am inclined to refer it to the OpTiidonais serpen- 

 tina of Gervais, Nais serpentina of some other writers. 



In the possession of a case formed of debris and mucous secre- 

 tion, presence of touch-organs, and arrangement of alimentary 

 canal, however, this species comes so near Yejdovsky's Slavina, 

 that had he observed the touch-organs, he would probably either 

 not have founded his new genus, or have done away with the 

 genus Ophidonais. 



