1904.] NATURAL SCIENCES OF PHILADELPHIA. 501 



long; reduction in length takes place at both ends and the setae tufts 

 descend to a correspondingly lower level. All abdominal tori are 

 shorter than the last thoracic and they diminish gradually and con- 

 stantly to the posterior end. They are especially prominent dorsally 

 where they terminate in a prominent projection marked with a con- 

 spicuous black spot. 



All setae are nearly colorless, translucent and striated. Those of the 

 first or collar fascicle are all of one form, slender, narrowly lanceolate, 

 slightly curved and with a single narrow wing, but differ consider- 

 ably in length. On other thoracic somites those in the dorsal rows of 

 the bundles are similar (PI. XXXVIII, fig. 38), but the ventral ones 

 (PI. XXXVIII, fig. 39) are shorter, spatulate, doubly winged, and have 

 acute but not mucronate tips; they differ somewhat in curvature and 

 breadth of wings, but the one figured is typical. The abdominal setae 

 are again all of one kind, rather more broadly lanceolate than, but 

 otherwise similar to, those of the collar fascicle. 



The thoracic uncmi are of two kinds — large aviculae and smaller 

 pick-shaped hooks, arranged in opposed parallel rows, there being 105 

 of each on II, 97 on V, and 90 on VIII on the type specimen. The 

 aviculse (PI. XXXVIII, fig. 40) are of a very pale yellow, the bases 

 long, slender, slightly curved ; the neck and head prominent and erect, 

 slightly inclined forward; the breast prominent, hemispherical; the 

 neck slightly tapered and about as long as thick at the base, the head 

 scarcely enlarged with the rather stout but acute beak strongly bent 

 downward, the crest little elevated and forming a dense sheath of fine 

 spines arranged in numerous transverse and longitudinal rows closely 

 appressed on the upper half of the beak. Abdominal aviculse differ 

 only in their somewhat shorter bases and less prominent breasts. They 

 are not associated with pick-shaped uncini and the type specimen has 

 about 80 in each torus. 



The pick-shaped uncini (PI. XXXVIII, fig. 41) have stems about as 

 long as the bases of the aviculae, but much more slender; they are 

 nearly straight, but more or less slightly enlarged and bent at about the 

 beginning of the outer one-third. The tip curves to a short blunt 

 point enclosed within a loose expanded hood, from which arises a deli- 

 cate, colorless, very slender process, making an angle of about 60° 

 with the stem. 



Except as already described for the branchiae, all pigment has faded 

 out. Distylia Quatrefages is employed instead of the earlier Bis'pira 

 Kroyer, because the author of the latter seems never to have applied 

 the name to any species. 



