[31] ANNELIDS OF PROVINCETOWN, MASS. 729 



line is reached, when the basal part becomes smaller, the outer part 

 longer, with a slight increase in its diameter. Back of the dorsal cirri 

 of the anterior segments is a thin plate, with convex margin, in front of 

 which the setae arise. This plate exists on all segments, but after a 

 few of the anterior becomes narrower, longer, conical (fig. 69). 



The ventral cirri of the first four segments are a little smaller than 

 the dorsal cirri ; they have a straight upper, a convex lower, margin ; 

 behind them is a plate or lobe similar to the dorsal ramus ; back of 

 the fourth segment the cirrus disappears, and the ventral ramus moves 

 gradually towards the ventral margin (fig. 69). After the fourth seg- 

 ment a projecting, arched plate, similar to the ventral ramus, i» found 

 about half way between the two rami. 



From the sixth segment a membranous densely ciliated ridge (fig. 68) 

 connects the bases of the opposite dorsal cirri. At first this ridge is 

 quite low, but afterwards becomes well marked. 



The dorsal setae of the anterior segments are very long (fig. 70), deli- 

 cate, margined on one edge; they shorten a little backwards, but behind 

 the middle again increase in length. 



The ventral setae (fig. 71) are shorter, more curved, and a little wider ; 

 in other respects similar to the dorsal setae. On the sixth segment the 

 ventral setae change to uncini (fig. 72). These project very slightly. 

 There are a few capillary setae at the lower end of each series of uncini. 

 The anal segment is bluntly rounded, with two delicate filiform cirri. 



On the anterior segments the dorsum is flat ; the sides and ventral 

 surface convex ; further back the dorsum becomes convex ; the sides 

 nearly straight ; the ventral surface flat, or slightly convex. 



General color of the body red ; head, sides of body, and feet, i^liite. 

 Only two specimens were found. 



Length of largest specimen, 21™°^. 



Width, 1^^. 



Number of segments, 82. « 



Found at Wellfleet, in sand, at low water. 



POLTDOEA Bosc. 

 PoLYDORA LiGNi Webster. 

 Annel. Ch»t. of New Jersey, etc., p. 119, pi. v, figs. 45-47. 18fi0. 



Our specimens were found living on the valves of Pecten irradianSy 

 their tubes occupying the spaces between the ribs. 

 Low water; not common. 



POLYDORA CONCHARUM VerHll. 

 Proceedings of the United States National Museum, p. 174. November, 1879. 



This large and peculiar species was very common, from near high, 

 water mark to 30 fathoms. 



