1904.] NATURAL SCIENCES OF PHILADELPHIA. 159 



sinus is very open with nearty straight parallel sides. On the abdomi- 

 nal somites these iincini (fig. 40) differ in the much reduced posterior 

 I^rocess, the deeper, more sloping breast and the more wedge-shaped 

 sinus. The figure is, however, somewhat foreshortened. The smaller 

 imcini (fig. 2) have a peculiar form, which is transitional between the 

 avicular and the usual pick-shaped uncini. The slender stem or body 

 is bent strongly and slightly thickened, but lacks a distinct breast. 

 The head is slightly enlarged with a very short, stout, slightly de- 

 curved beak and a prominent cap-like crest, much subdivided; from 

 the base of the beak projects a slender angulated filament. In the 

 form of the small uncini this species departs widely from the typical 

 Sabellce. 



Suruga Bay, 3,707, 63-75 fms. Type and one other. 



Potamilla acuminata n. sp. (PI. XI, figs. 3-6; PI. XII, fig. 41.) 



This species is elongated and slender, a complete example having a 

 total length of 56 mm., of which the branchise are 20 mm. and the 

 thorax 5 mm., the diameter being 1.9 mm. 



The branchiffi are more than ^ of the total length, and when retracted 

 into the tube are not at all or very slightly twisted and coiled. Two 

 specimens have 19 radioles on the right, 17 on the left, the other having 

 15 and 16 respectively. They are straight, slender, of nearly uniform 

 diameter, without eye-spots, and bear barbs nearly or quite to the tips 

 in the dorsalmost radioles, but have a free end devoid of barbs and of 

 considerable length in the ventral ones. Most of the radioles are pro- 

 vided with a short membranous wing on the inner side of the base, but 

 there is no trace of a connecting web. The barbs have the usual 

 biserial arrangement and equal or exceed the diameter of the body, 

 with little diminution toward the distal end. The bases are entirely 

 simple. 



The collar is scarcely evident dorsall}', but becomes prominent 

 opposite to the dorsal setse line, just below which is a barely distinguish- 

 able fold. On each side of the median ventral line is a broadly roiuided, 

 flat, somewhat tliickened process, about as long as the first somite. 

 In the retracted specimens these overlap medially. The entire ventral 

 portion of the collar, except the ventral lobes, is extremely thin and 

 delicate. 



Between the bases of the branchise is a small roimded prostomial 

 lobe, from which a broad folded memibrane extends laterally around 

 the mouth and joins the bases of the branchise. Connected with the 

 inner side of the latter also are the so-called tentacles, consisting of a 

 pair of processes about twice as long as the second somite, with the 



