48 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 10 



Rhamphobrachium longisetosum Berkeley 

 Plate 1, Figs. 1-8 



Berkeley, 1938, pp. 428-436, 8 figs. 



Collections.— ^\2^-3^ (1); 890-38 (1, with tube); 908-38 (1) 

 981-39 (2); 1008-39 (3); 1010-39 (23 anterior ends); 1012-39 (2) 

 1018-39 (1) ; 1020-39 (12) ; 1023-39 (1) ; 1125-40 (2) ; 1130-40 (4) 

 1131-40 (1); 1149-40 (1); 1178-40 (2); 1182-40 (1); 1245-41 (1) 

 1251-41 (1); 1264-41 (1); 1265-41 (2); 1267-41 (3); 1289-41 (1) 

 1290-41 (1); 1299-41 (2); 1316-41 (1); 1321-41 (1); 1411-41 (1) 

 1412-41 (1); 1435-41 (1). 



R. longisetosum has heretofore been known through only an original 

 description, based on 2 small anterior ends that measured only 4 and 18 

 mm long (Berkeley, 1938) ; an additional account is therefore given. 

 Length of an individual that may be nearly two thirds complete is 53 

 mm; another larger anterior end of 45 setigers measures 32 mm long; 

 another of 50 setigers is about equally long. The prostomium has 2 pairs 

 of tiny black eyespots at the base of the inner lateral tentacles, along the 

 anterior and outer lateral sides. The frontal antennae are depressed 

 spherical; the occipital tentacles are short, the ceratophores with 4 or 5 

 shorter articles and a longer distal one ; their styles are smooth, taper dis- 

 tally. 



The first 3 pairs of parapodia are progressively enlarged, the third 

 much the largest; all are directed anteroventrally. The segments from 

 which they arise, however, are only about as long as those following. Ven- 

 tral cirri of the first 3 setigers taper rapidly from thick bases to bluntly 

 pointed tips; they increase in length from the first to the third, all com- 

 pare favorably in size with their respective dorsal cirri. The other para- 

 podial lobes on the first 3 pairs of parapodia are variable in length or ap- 

 pearance, owing to the varying amount of setal projection. On some speci- 

 mens the setae are completely retracted, their respective lobes correspond- 

 ingly withdrawn ; on others the lobes are very conspicuous and the long 

 setae project for a distance greater than that of the entire anterior portion 

 of the body. From the fourth setiger the ventral cirrus is represented only 

 by a pale, glandular pad. 



Branchiae are present from the eighth or ninth setiger, as a simple 

 filament, continued so through the fourteenth; there are 2 filaments on 

 the fifteenth, 3 on the eighteenth, 4 on the twentieth, the arrangement 

 neatly pectinate, 5 or 6 filaments on the twenty-second, increasing to 8 or 

 10 filaments in a median region (pi. 1, fig. 3) and probably continued 

 through much of the body length. 



