NO. 2 HARTMAN, BARNARD: BENTHIC FAUNA OF DEEP BASINS 131 



Ilyphagus Chamberlin was erected for 3 species, all originating in 

 deep water. /. bythincola Chamberlin (1919b, p. 402) was taken off 

 western Mexico in 1380 fms; /. ascendens Chamberlin (1919b, p. 403) 

 off the Galapagos Islands in 633 fms, and /. pluto Chamberlin (1919b, 

 p. 403) off Peru in 2845 fms. The types are in the United States Na- 

 tional Museum, where they have been reexamined. They agree with one 

 another mainly in that they are densely coated with long papilla en- 

 crusted with gray mud. The setae are long, slender and distally entire; 

 all are cross-barred along their free lengths. None of the specimens has 

 the cephalic structures extended and all are too brittle to dissect. 



/. bythincola, the genotype, is a very flat, depressed, solelike form ; 

 it is oval in shape, broadly rounded at either end and measures to 50 mm 

 long. Neuropodial setae are much coarser than notopodial ones and they 

 taper distally, terminating in a long, fine, straight or slightly curved tip. 

 On the holotype specimen, most of the setae have been broken off at the 

 base, but those that remain are as originally described. Parapodia are 

 lateral or ventrolateral in position. Neuropodial setae are about four and 

 a half times as thick as notopodial setae but a little less than half as long. 

 The annulations of notopodial setae, near the tip, are about as wide as 

 long, and increase to five times as wide as long at the base. In neuropodial 

 setae the proportions differ in that the bars are two and a half times as 

 wide as long near the tip, and about five times as wide as long at the 

 base. All setae have distal tips that are slender and pointed. 



/. ascendens is similarly thickly covered with papillae on dorsal and 

 ventral sides, encrusted with mud to near the tips of the papillae. The 

 general shape of the body is that of a slightly depressed cucumber meas- 

 uring 55 mm long. A pair of conspicuous parapodia at the anterior end, 

 dorsolateral in position, retains a very long seta that extends distally, 

 back to the end of the body; bases of other setae, perhaps similar, form 

 an oblique series numbering about 6 on a side, with the medialmost in 

 posterior position and gradually extending forward to the outermost 

 setae. The setae of this first segment are the longest and thickest of any 

 retained on the specimens. This feature sets the species apart from others 

 ascribed to the genus. All other setal fascicles can be seen only in ventral 

 view of the body. The neuropodial ridges form paired series of trans- 

 verse rows, at first in longitudinal series with the first parapodium (best 

 seen in frontal view of the body) and gradually approaching medially 

 to form nearly semicircular series at the posterior end of the body. These 



