190 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



In the male, the first 20 somites form the anterior body region. 

 The first three dorsal cirri are acute oval in outline, with filamentous 

 apices and the ventral ones are similar to them in form but are 

 smaller. (Fig. 14.) The fourth and fifth cirri are more elongated 

 but retain in general this distinction between the basal portion and 

 the filamentous tip, while from the sixth to the twentieth the cirri 

 are long and slender, reaching beyond the tips of the setae. (Fig. 15.) 

 In these somites the setae lobes become heavier and blunter than 

 farther forward but in other respects they do not noticeably differ. 



In the modified region characteristic heteronereis changes appear 

 as indicated in Figure 16. 



In the anterior region of the male are two kinds of setae. The 

 first, found in both noto- and neuropodium, has a long slender, eam- 

 erated shaft and a very long delicate, terminal joint which narrows 

 to a very sharp point and has a row of teeth along one margin. The 

 second variety, found only in the neuropodium. is similar to the first 

 in the form of its shaft, but the terminal joint is blunt-pointed and 

 short, with a row of stiff spines along one margin. (Fig. IT.) These 

 spines are as long as the transverse diameter of the main part of the 

 terminal joint. In the modified portion the setae have the form 

 characteristic of this state; a prominent camerated shaft and a 

 broad, oval terminal joint toothed along one margin. 



In the females the number of modified somites varies from 18 to 

 25. The females have a setal and parapodial structure essentially 

 like those of the males except that the distinction between the first 

 three, and the later dorsal cirri is much less marked. The larger 

 female are about 35 mm. long and the males about 25 mm. 



Family SABELLARIIDAE 



MONORCHOS, new genus 



Body-form characteristic of the family : Opercular lobes fused ex- 

 cept for a shallow median ventral incision. On the margin of each 

 opercular lobe is a single row of paleae, the two rows overlapping 

 at their ventral ends but separated dorsally. A single pair of dark 

 brown heavy hooks lies in the space between the dorsal ends of 

 the rows of paleae. On the dorsal median surface of the fused 

 opercular lobes are two rows, each three or four in number, of short, 

 sharp dark brown spines, arranged in an inverted V with the apex 

 near the margin of the ventral incision. On the ventral surface the 

 opercular stalk is folded so as to form a deep groove leading back 

 to the mouth. A single row of tentacles lies on either margin of this 

 groove. Just anterior to the mouth is a pair of long palps, capable 

 of being retracted into the groove. 



