1883.] NATURAL SCIENCES OF PHILADELPHIA. 20Y 



anterior segments, are about 0"05 to 0'06 mm. long, and consist of 

 a long curved handle, ending in a small recurved hook. 



The podal hooks of the posterior three setigerous segments 

 form close transverse, rows, fig. 6, of variable number, from 9 to 

 24 in each row. The hooks are minute, and measure from 0*025 

 0'03 mm. long. They consist of a broad handle, ending in a lateral 

 comb-like extremity, as represented in figure 7. 



The number of podal seta and podal hooks is more or less 

 variable in the corresponding segments of different individuals, 

 and frequently also on the two sides of the segments of the same 

 individual. The difference is due sometimes to the accidental 

 loss of some of the appendages ; sometimes probably to circum- 

 stances interfering with their development. In several specimens 

 the following differences were observed : 



Specimen 1. 



First segment, 6 and 8 setae. 



Second to fourth segment, inclusive, 8 to 10 setae and 4 to 5 hooks. 



Fifth to eighth segment, inclusive, 6 to 8 setae and 4 to 5 hooks. 



Ninth segment, 6 setae and 9 and 22 hooks. 



Tenth segment, 4 setae and 12 and 18 hooks. 



Eleventh segment, 3 and 4 setae and 12 hooks on each side. 



Specimen 2. 



First segment, 8 setae on each side. 



Second to sixth segment, inclusive, 8 setae and 4 hooks on each 



side. 

 Seventh and eighth segments, 6 or 7 setae and 4 hooks, except on 



one side of the eighth segment, in which another fascicle of 6 



setae substituted the usual fascicle of hooks. 

 Ninth segment, 6 setae on each side and 9 and 20 hooks. 

 Tenth segment, 4 and 5 setae and 13 and 16 hooks. 

 Eleventh segment, 3 and 4 setae and 12 hooks on each side. 



Specimen 3. 

 First segment, 8 setae each side. 

 Seven succeeding segments, 6 to 10 setai and 3 to 4 hooks each 



side. 

 Ninth segment, 7 setae and 24 hooks each side. 

 Tenth segment, 3 setae and 18 hooks, but on one side the latter 



were all imperfect, mostly with the comb undeveloped. 

 Eleventh segment, 2 setae and 14 hooks each side. 



