FRESH-WATER NEREIDS FROM THE PACIFIC COAST AND HAWAII. 209 



rapidly diminishing towards the small prostomium, and very gradually towards the 

 pygidium. The club shape is much less apparent in large specimens. The somites 

 are 75 in a large example. The trunk is considerably depressed (PI. XVII, Fig. 29). 

 The posterior region is so fragile that few complete specimens are obtained. 



Except perhaps for its small size, the prostomium (PI. XVI, Fig. 1) presents no 

 unusual feature. It is two-thirds as broad as long; the palpi extend considerably 

 in front of the tips of the antennae, which are decidedly short, not exceeding one- 

 third the length of the prostomium. The peristomial cirri (Fig. 1) are likewise very 

 short for this genus, the longest pair (posterior dorsal) extending over no more than 

 three and one-half somites, and are less than the transverse diameter, even in young 

 examples. The eyes are black, large, and conspicuous, the posterior pair are slightly 

 nearer the median line than the anterior. No lens has been detected even in sec- 

 tions. The peristomium deviates from the typical form for the genus in being little 

 if any longer than the somites immediately following. 



The proboscis is armed with paragnaths of the usual type (Figs. 2, 3) which 

 exhibit the typical form and arrangement for the genus Nereis. 



The parapodia (Figs. 4, 5, 6) are rather long for the diameter of the body. Pos- 

 teriorly this is especially striking on account of the tapering of the trunk. In none 

 of the specimens that I have seen is there any indication of the "epitokous" or "het- 

 eronereis" condition. The worm attains sexual maturity in the ordinary or "ato- 

 kous" state. The parapodia, therefore, as the figure of the fifth (Fig. 4), of the 

 thirty-first (Fig. 5), and of the sixtieth (Fig. 6), clearly show, form a uniform series, 

 becoming simpler posteriorly. 



In the most anterior region the dorsal ligules are large and triangular; the ven- 

 tral ligules are of the same form, but smaller. The dorsal cirrus springs from the 

 dorsal ligule, about one-third the distance out from its base; the ventral cirrus, almost 

 exactly the same size and shape as the dorsal, arises at the extreme base of the ventral 

 ligule. The dorsal lips are very unequal in size, the smaller bearing a fascicle of 12 

 to 13 setae; the other approximates the shape of the ligules. The ventral lips bear 

 two fascicles of setae supra- and infra-acicular of which the lower contains about 

 twice as many setae as the upper, and all but two of the falcate ones. 



The acicula are black throughout their length, are nearly parallel, tapering 

 towards the distal tips, which curve away from each other. 



As we pass towards the posterior extremity both ligules, but more particularly 

 the ventral, become smaller (PL XVI, Fig. 5); finally, in the most posterior para- 

 podia the ventral ligule becomes very much reduced, or may even disappear (Fig. 

 6). A corresponding reduction of the lips does not occur except in some of the most 



