266 bulletin: museum of comparative zoology. 



the others, the trunks stouter and longer, with two main limbs and a dense 

 brush of terminal branches. Total nimiber of segments in type near eighty- 

 five. 



Length, 110 mm.; width of thorax, 11 mm. 

 Locality. — Calif.: Crescent City (A. Agassiz). 

 Type.— M. C. Z. 2,135. Paratypes.— M. C. Z. 449. 



31. SciONiDEs DUX, sp. nov. 



Plate 3, fig. 9. 



As compared with the genotype {Terebella reticulata Ehlers) this is a very 

 much larger species easily differentiated as well by various other characters, 

 such as the structure of uncini which, while agreeing closely in more general 

 features, differ in numerous details. These have the basal shoulder more 

 remote from the crest, thus leaving the neck-region longer; the sinus wider 

 at bottom, the beak less divergent from principal axis. Differing from those 

 of reticulata decidedly in having the denticles of the crest in five series instead 

 of in four with the teeth of these series more numerous, the larger teeth of the 

 lowermost row, e. g., numbering six instead of only two. There are seven- 

 teen setigerous segments, bearing setae of simple limbate type, with no trace 

 of distal denticulations. The uncini begin on the second of these (V); they 

 are in single series on the first six pairs of tori and in a double interlocking 

 series on the remaining pairs. There is a non-setigerous tubercle below each 

 of the second branchiae (somite III), this well developed but much more 

 slender than the setigerous one. Tentacular filaments numerous, closely 

 crowded in a series across anterior edge of fold, flat and ribbon formed, long. 

 No eye-spots observable in types. Peristomium with labial edge below wide 

 and straight, a second edge farther caudad with elongate pit or depression 

 between the two. Branchiae three pairs on II, III, and IV. These ramose, 

 with thick trunks and principal limbs, and numerous fine terminal branches or 

 filaments densely grouped. The third branchiae are inserted obviously nearer 

 together than the second and first. Not differing in length but the second 

 branchiae with more abundant branches. First twelve ventral plates broad, 

 the first ones oblong, the others becoming trapeziform, the subsequent ones 

 very narrow. Plate of segment II longer than that of III and both much 

 longer than those of IV and V, the others increasing in length and decreasing 

 in width in going caudad. Number of segments in type seventy-five. 



Length, 125 mm. ; width across thorax, 10 mm. 

 Locality. — Calif.: Crescent City (A. Agassiz). 

 Type.— M. C. Z. 2,034. Paratypes.— M. C. Z. 228. 



