1906.] NATURAL SCIENCES OP PHILADELPHIA, 227 



broadened and end in two divergent, slightly curved points, the ventral 

 of which is the longer; w^hile below the dorsal is a serrated sheath, the 

 rather coarse teeth of which are directed outward. Seldom more than 

 three or four of the latter form occur in a parapodium along with ten or 

 fifteen of the former, 



Subacicular sets are all compound. The most numerous kind 

 occur to the number of about fifteen. They have moderately stout, 

 rather strongly curved stems, the end being very unequally and 

 obliquely bifurcated to form a socket, the dorsal border of which is 

 provided with a few teeth (fig. 20), while the blades are comparatively 

 short, but increase in length from the ventral to the dorsal margin of 

 the bundle, and have one border fringed and the end terminated by a 

 pair of distinct but not widely separated and nearly parallel teeth. 

 The second kind of compound setse (fig. 22) seldom exceeds three in 

 numl^er. They have the same construction as the more numerous 

 form but are much more slender and delicate in all their parts, and the 

 blade often equals the entire length of the neuropodium or about three 

 times the length of the longest blades of the other type. On the most 

 anterior segments the two forms appear to grade into each other. 

 The setse of this species differ decidedly from those of typical members 

 of the genus and are more nearly like those of Prionognathus ciliatus 

 Keferstein. 



These worms are quite colorless and their form and histological 

 structure indicates that they may be pelagic in habit. 



The type and a somewhat smaller cotype were obtained at Quaran- 

 tine Rock, Port Townsend, Washington, June 27, 1903. 



Notomastus giganteus. Plate X, figs. 24, 25. 



The only complete specimen measures 140 mm. in length and 7 mm., 

 in maximum diameter in the thoracic region, but a second incomplete 

 example is much larger. Even taking into account the contracted 

 state of the specimens, this species is much stouter than usual for the 

 genus. The body is nearly terete or slightly depressed and for the 

 first fifteen or twenty millimeters increases in diameter, and then falls 

 off to the posterior end which is two millimeters in diameter within 

 ten segments of the anus. 



The prostomium is a small rounded lobe bearing a minute conical 

 palpode and is completely retracted within the peristomium, which, 

 except in being slightly longer, resembles the immediately following 

 segments. The protruded and collapsed proboscis "forms a discoid, 

 wrinkled structure fully 8 mm. in diameter. All of the thoracic seg- 



