250 PROCEEDINGS OF THE ACADEMY OF [April, 



teeth and a marginal mucron (PL XV, fig. 22). Most numerous are 

 the compound setae (fig. 21) which are arranged in about six rows, are 

 pale yellow, with curved and distally thickened shafts and short, 

 strongly hooked, and bidentate appendages with a delicate guard 

 finely denticulated on the margin. The last become larger caudad. 

 Beginning at about XXVII two (sometimes one) stout crochets appear 

 projecting prominently obliquely from the neuropodium ventral to 

 the compound setae; they are slightly curved, with stout principal 

 tooth and smaller more distal accessory tooth and provided with a 

 split guard (fig. 23). 



Branchiae strictly unilateral pectinate throughout (PL XV, fig. 20), 

 consisting of a tapered main stem arising from the base of the neuro- 

 cirrus on its dorsal side and curving gently up the sides of the body, 

 but remaining erect, leaving the dorsum uncovered ; filaments arising 

 nearly at right angles to the stem in a close rank and lying nearly 

 parallel, slender, the longest not exceeding two-thirds the length of 

 the notocirrus and the main trunk, exclusive of the terminal filament 

 into which it is prolonged, not much greater. On the type the gills 

 begin on somite IX with seven filaments, attain the maximum of 

 twelve filaments and retain this number, with occasionally one or two 

 more for a great many segments, then undergo gradual reduction 

 posteriorly, the gill on the fourth preanal segment still being trifid. 



With few exceptions the gills of all specimens begin on IX, the only 

 departures being three specimens, on two of which the first on one side 

 occurs on VIII and on another on X. The number of filaments 

 varies greatly, increasing with the size of the specimen. The smallest 

 example (1 mm. wide) has the first gill simple and most of the others 

 bifid. A complete specimen, 47 mm. long and 2 mm. wide with 87 

 segments, bears gills on all podous segments beginning with IX, the 

 first and the last two consisting of a single filament each and the 

 maximum number of filaments being three. One 140 mm. long and 

 4 mm. wide lacks gills on the last four segments, the maximum number 

 of filaments is seven and most of the gills caudad of the middle of the 

 body are trifid. Another, 195 mm. long and 7 mm. wide, with 177 

 segments, has trifid gills on IX of one side, X of the other and attains 

 a maximum of twelve or thirteen filaments, with the last three seg- 

 ments abranchiate. The largest complete specimen is 203 mm. long 

 and 9 mm. wide and bears a small gill of two filaments on one side 

 of VIII, the maximum number of filaments being fourteen and the 

 last gill on the fourth preanal segment. Bifid filaments occur fre- 

 quently. 



