CHAMBERLIN : PACIFIC COAST POLYCHAETA. 265 



In the posterior thoracic uncini the base shows a distinct angulation or shoulder 

 at or toward the base of the neck in place of the triangular median process 

 shown in alata. This shoulder is also present in the smaller abdominal un- 

 cini; it is more abrupt and prominent, less gentle and rounded than in fratrella 

 while it is quite absent in alata. The beak in the manubriate uncini is more 

 divergent than in fratrella. 



Greatest width, 3 mm. The specimen incomplete posteriorly- 

 Forty-nine segments in the two pieces present. 

 Locality. — Calif.: Mendocino (A. x\gassiz). 

 Type.— M. C. Z. 502. 



29. EuPOLYMNiA REGNANS Chamberlin. 



Mem. M. C. Z., 1918, 48, p. 433, pi. 79, fig. 1-3. 



One large and several partly grown specimens of this species were 

 collected by Mr. Agassiz at Panama, the type-locality, where the 

 species is apparently common. 



30. EuPOLYMNIA CRESCENTIS, Sp. nOV. 



Plate 3, fig. 6, 7. 



This species differs from the widespread Indo-Pacific E. trigonostoma 

 Schmarda (syn. P. congruens Marenzeller) and other previously described 

 species in the form of the uncini. The uncini as compared with those of 

 trigonostoma are much more slender, evenly curved, with the beak propor- 

 tionately longer, reaching nearer to the end of the plate; the subrostral process 

 nearer the end away from the base of the beak, farther removed from tip of 

 beak; the basal projection or shoulder small, much slighter than in trigono- 

 stoma. Just caudad of the tentaculiferous fold are numerous minute dark 

 eye-spots. Tentacles crowded, numerous and long; slender; each with the 

 usual longitudinal groove. Segmental papillae present only on segments 

 III, IV, and V. Of the thoracic uncinigerous tori the first six bear the uncini 

 in single simple series, the others in a double, interlocking series. Seventeen 

 setigerous somites present. Ventral thoracic plates very wide, trapeziform, 

 the lateral ends being angularly pointed; the anterior ones rather more than 

 twice as wide as the length of the adjacent row of uncini; caudad the anterior 

 margin becomes more decidedly convex; on II, III, and IV they are not set 

 off from the lateral region; these plates roughened; caudad of XVI, plates 

 reduced and longitudinally divided. First branchiae decidedly longer than 



