206 PROCEEDINGS OF THE ACADEMY OF [-^lay, 



iinbranched. They contain large axial Ijlood vessels, from which pin- 

 nate loops branch on either side, corresponding with slight surface 

 plications. 



Capillary setse alone are found on both rami of parapodia of the 

 branchial region. They form broad spreading fan-shaped tufts and 

 are very numerous (40 or more notopodials and even more neuropodials) 

 and arranged in two vertical rows, a long seta of the posterior being 

 always paired with[|a shorter one of the anterior row ; much the longest 

 and most slender in dorsal part of notopodium, stouter in ventral part 

 of both rami. All setse are pale yellow with tapering, longitudinally 

 striated stems finely granulated on the surface, with more or less 

 prolonged and delicate tips and the more or less well developed wings 

 or margins directed toward the middle part of the foot on both rami 

 (fig. 33). Wings best developed on dorsal neuropodial and ventral 

 notopodial setse, the marginal setse of both bundles nearly lacking 

 them. Notopodial setse of II very small and delicate, those of the two 

 sides crossing over the prostomium. As the foliaceous structures and 

 gills become smaller the setse also become smaller and fewer. Crochets 

 appear in the ventral portion of the series on neuropodia of the post- 

 branchial region. There are 2 on XLI and 6 on XLIII. They (fig. 24) 

 are nearly colorless, rather slender, delicately striated longitudinally, 

 the tips gracefully hooked, with a stout beak surmounted by an 

 accessory process, both enclosed in a delicate hood conforming to their 

 contour. 



The type is No.l, 055, Coll. Acad. Nat. Sci. Phila. ; found with Aricia 

 fimhriata, taken at Albatross Station, No. 5,771, off Honshu, Japan, 

 on June 5, 1900; 61 fathoms; bottoms of green sandy mud. 



From the type of the genus, S. cirratus Webster and Benedict, 

 known only from Eastport, Maine, this species differs in having 

 numerous pairs of gills beginning on III, instead of 13 pairs only 

 beginning on IV, in having 1 pair of large eyes instead of 2 pairs of 

 small ones, and in the much larger size. 



Explanation of Plates XV, XVI. 



Plate XV. — Pi-ionnspio heterobrnnchia — figs. 1 to 6. 



Fig. 1. — Dorsal aspect of head and somite II, sliowing scars of attachment 



for tentacular cirri and gills. X 40. 

 Fig. 2. — Anterior aspect of parapodimii II wdth seta? and detached gill of 



other side. X 98. 

 Fig. 3. — Similar view of parapodium and gill of IV, without sette, X 98. 



Only a few of the transverse bloodvessels and external ridges are shown. 

 Fig. 4. — Anterior aspect of parapodium X. X 98. 

 Fig. .5. — Posterior aspect of detached gill of VI. X 98. 

 Fig. 6. — A crochet from neuropodium of L. X 600. 



