474 PROCEEDINGS OF THE ACADEMY OF [June, 



venter flat, with a neural groove, but near the caudal end the body is 

 more depressed. 



The single pair of branchiae, which arise as indicated above from 

 the 4th somite, are large and conspicuous and divided into numerous 

 filaments, wdiich are so crowded that they appear to arise together 

 from a common point, but which really spring in a unilateral pinnate 

 fashion from a spirally wound stem. The latter makes about 3 turns, 

 but owing to the closeness of the filaments, the bases of which are in 

 actual contact, the number is somewhat uncertain. In line with the 

 branchicT somites II and III both bear dorsal tubercles, which are 

 especially prominent on III, on which, in both specimens, a second 

 smaller tubercle occurs at the base of the larger one ; these are prob- 

 ably reduced gills, and, were it not for the exact correspondence of the 

 two specimens, might be supposed to be regenerating. 



On somites VI, VII and VIII short but prominent processes are 

 present between the setigerous and uncigerous tori, just behind the 

 setae line. A small sense-organ may be found in a corresponding posi- 

 tion in relation to most of the posterior parapodia. 



Setse begin on IV as a small tuft high up at the foot of the dorsal fold. 

 On all remaining somites the parapodia are ventro-lateral, but as the 

 uncigerous ridges are much longer on the anterior than the posterior 

 thoracic somites, the slender setae are at first more elevated in position, 

 and gradually sink as the uncigerous tori diminish in extent. The 

 abdominal parapodia have the base contracted and the dorsal angle 

 somewhat produced. 



Slender setae are found on 17 somites, from IV to XX inclusive, are 

 rather few in number, especially on IV, and are always arranged in a 

 short compact vertical row. The shafts are pale yellow, fibrous, rather 

 long, more or less strongly curved in a sigmoid fashion toward the end, 

 with a mucronate tip, below which each side is provided for a short 

 distance with a rather broad, delicately striated wing with entire 

 margin terminated rather abruptly at its distal end. Different setae 

 differ greatly in their curvature and the extent of the wings, some being 

 nearly straight with almost symmetrical wings, others almost angulated 

 with the greatest width of the wings alternating. Uncini are found 

 in all somites except the first four. In the thoracic region they face 

 alternately backward and forward, and interlock in a double row, are 

 nearly colorless, with short somewhat triangular bases, a short neck, 

 narrow sinus, strongly hooked, stout, acute rostrum and an apical crest 

 of 5 transverse rows of spines, the lowermost consisting of about 4, the 

 others much more numerous, up to 10 or 12. In the abdominal region 



