NO. 3 HARTMAN I ORBINIIDAE, APISTOBRANCHIDAE, PARAONIDAE 221 



light, due to internal structures. The spinelets have their origin from 

 longitudinal fibrils lying within the shaft. They can be traced inward to 

 the core, where they are separated by clearer areas. The number of spine- 

 lets in a transverse row for a single seta, from base to tip, remains fairly 

 constant but the spinelets are thicker and shorter at the base and longer 

 and slenderer at the tip. These setae have been called also capillary setae, 

 camerated capillaries, awl setae and other descriptive names. 



Furcate, lyrate or forked setae (pi. 22, figs. 7, 8) are usually present 

 only in notopodia of the abdominal segments and some posterior thoracic 

 notopodia, or they are absent. They are usually few in a fascicle and 

 located in an inferior position, accompanied by pointed setae. Each con- 

 sists of a straight cylindrical shaft, smooth or spinous along its outer 

 side, two long diverging tines connected with each other by a thin, 

 translucent membrane that may be pouched (best seen from the edge of 

 a tine), and strengthening fibrils extending out from the shaft. When 

 perfect, the thin connecting membrane may be neatly serrated or crenu- 

 lated at its free edge (pi. 20, fig. 5) ; when worn, it is frayed, torn or 

 altogether lacking. The dimensions and positions in the fascicle suggest 

 that these setae function to keep clean the long pointed setae. They may 

 occur more often than reported as their sparse number and small size 

 make them difficult to find. 



Uncini or uncinate hooks of characteristic form are found in thoracic 

 neuropodia of some species. They may form thick conspicuous palisaded 

 vertical series, most numerous in middle and posterior thoracic seg- 

 ments. Each is straight or distally curved or has a tip that is blunt, 

 entire or divided. There may be a delicate hyaline hood (pi. 22, figs. 5, 

 6) or the tip may be uncovered. The outer curved region may be smooth 

 (pi. 35, fig. 6) or have transversely ridged (pi. 20, figs. 3, 4) or denti- 

 culated (pi. 40, fig. 4) structures. Uncini are present in some species of 

 Orbinia, Phylo, Scoloplos, Scolaricia and Orbiniella. They are absent 

 from Haploscoloplos, Califia and one species of Naineris. They are 

 peculiarly curved and have a rostrate tip (= swan-shaped hooks) in 

 Proscoloplos. Cauduncini ("Zipfelhaken" of Eisig, 1914, p. 216) are 

 hooded uncini, as the name implies ; they are described for species of 

 Protoaricia (Eisig, 1914, p. 216) and Naineris (Annenkova, 1931, p. 

 204). 



Subuluncini (pi. 37, figs. 5, 6) are transitional between pointed setae 

 and uncini ; the base or stalk is uncinate, the distal end abruptly slen- 

 derer and long pointed. The outer side of the curved region may be 

 ornamented with rows of spinelets. They are known from some species 

 of Naineris and Protoaricia. 



