NO. 4 HARTMAN: POLYCHAETOUS ANNELIDS 425 



The thorax consists of 12 segments; each is more or less clearly bian- 

 nulate. The first or peristomial segment is achaetous and apodous. The 

 second one has a dorsal fascicle of capillary setae but no visible neuro- 

 podium (hence the specific name). From the third segment, notopodia 

 and neuropodia are present; the 2 branches are widely separated from 

 each other. This arrangement continues through the last 10 thoracic 

 segments. Lateral organs, as typical for the genus are present on all 

 thoracic and abdominal setigerous segments ; they are located nearly mid- 

 way between notopodia and neuropodia but slightly nearer the former. 

 Those in abdominal segments are noticeably the larger. There are 4 

 pairs of nephridial pores at the sides of the body, along a lateral depres- 

 sion and in the grooves that separate segments 8/9, 9/10, 10/11 and 

 11/12 but they are inconspicuous and can be seen only by pushing the 

 segments apart. None have been found on the abdomen; this species is 

 therefore referred to the subgenus Clistomastus. 



The first abdominal segment is slightly thicker than, and about as 

 thick as, the last thoracic one. It has transverse wrinkles of contraction. 

 Both notopodial and neuropodial tori are provided with only simple 

 hooded hooks, disposed in single rows. Abdominal notopodia of a pair 

 approach each other at the middorsum so that their glandular ridges are 

 adjacent. Neuropodia, however, are lateral to ventrolateral in position 

 and have longer glandular ridges and tori. In anterior abdominal seg- 

 ments the superior edge of neuropodia is slightly elevated to form a small 

 papilla ; this is less conspicuous farther back. 



Hooded hooks have a long, straight shaft except for the thick node 

 near the middle. The fang is strong and sharply curved downward ; it is 

 surmounted distally by a row of 5 or 6 fine teeth. The hood neatly sur- 

 rounds the beak; its aperture is small and oval. 



No distinct branchial structures or genital pores have been identified; 

 they are believed to be absent. Respiration is perhaps accomplished only 

 through the surface epithelium. Gonadial products may be released from 

 the body only by autotomy or rupture of certain segments. 



Notomastus (Clistomastus) hemipodus is characterized in having the 

 thorax areolated through only the first 5 segments; the first setigerous 

 segment lacks neuropodia. Lateral organs are present throughout. 

 Nephridial apertures number only 4 pairs and are present in posterior 

 thoracic segments. Prcstomial eyes consist of a single pair of spots in 

 front of the nuchal slits. Hooded hooks terminate in a strong, recurved 

 fang surmounted by 5 or 6 teeth in a single transverse row; the hood is 



