250 PROCEEDINGS OF THE ACADEMY OF [April, 



cirri, the ventral about as long as the segment, the middle about two- 

 thirds as long, and the dorsal more than twice as long, slender distally 

 and resembling the branchiae, with which it stands as the first of a 

 series. 



The remaining three thoracic segments are a little longer and IV 

 and V bear distinct ventral glandular plates. Their neuropodial setse 

 are stouter than those on I and II, but have no associated cirri and 

 arise from the anterior margin of the segment on a level about mid- 

 way between the neuropodial tufts of I and II. ' Each of these seg- 

 ments bears a dorsal cirrus or gill similar to that on II and in line with 

 it, leaving a broad, naked area on the dorsum. Unlike II these somites 

 bear no middle cirrus, but in place of it a prominent vertically elongated 

 notopodial tubercle bearing a vertical series of large, coarse, paddle- 

 shaped setse. 



Abdominal segments are somewhat flattened and only obscurely 

 separated. As indicated above they decrease gradually in both 

 length and diameter to the caudal appendage. Dorsally they present a 

 somewhat arched area between the rows of gills and ventrally are 

 excavated by a deep groove for the fecal tube, which is held in place 

 by the tufts of slender neuropodial setae crossing from side to side 

 beneath it. 



The body walls are exceedingly thin and delicate in the dorsal 

 median area and permit the intestine to show through distinctly ; the 

 sides and ventral parts are decidedly thicker and more muscular. 

 The abdominal gills have the same general form and position as the 

 thoracic but are more perfect in structure, having larger blood-vessels, 

 thinner walls and more numerous and prominent transverse cihated 

 ridges along their medial aspect. The first five or six are also much 

 longer and have a length equal to the width of the interbranchial area. 

 From this point they decrease in size very gradually and are totally 

 absent from the last five or six segments. 



On the first abdominal segment the parapodia are very extensively 

 developed and the notopodial uncinigerous tori occupy the entire 

 side of the segment from the branchia nearly to the ventral median 

 line. Ventrally they become higher and terminate in a small free 

 lobe, from beneath which arises a delicate ventral cirrus, and below 

 this again the small neuropodial tubercle with its tuft of setse. The 

 tori decrease in length chiefly from the dorsal end, at first very slowly, 

 then rapidly and at the same time become more sharply defined as 

 distinct, thin, outstanding lobes bearing the uncini on their margins. 

 Toward the posterior end they become merely small prominent pro- 



