180 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



setse above, and a row of about three spines below ; on tlie fourth and 

 fifth segments there are six to nine uncini in the row, and more far- 

 ther back, where they become prominent, strongly hooked, or claw-like 

 uncini. The fourth and several succeeding segments are usually more 

 than twice as long as broad, with an annulatiou in front of the middle ; 

 farther back, in the middle region, the segments are six to eight times 

 as long as broad, very slender, swollen near the posterior end, where 

 the setse arise. The last three setigerous segments are about as long as 

 broad, swollen in the middle, and bear slender seti© about one-half as 

 long as the breadth of the body, and a row of uncini. Anal segment 

 consohdated with the preceding, apparently single, non-setigerous one, 

 very obliquely truncated at the end, and surrounded by a well-developed, 

 smooth border, interrupted dorsally, so that when expanded it has a 

 spatulate form. The anal opening appears to be nearly central, within 

 the border. The caudal membrane is filled with blood-vessels. In the 

 middle region of the body, on the ninth to eighteenth segments, in the 

 upper fascicles of acute setae, are two very long, slender, flexible, thread- 

 like setse, usually unequal, the longer six to eight times as long as the 

 diameter of the segments 5 they are covered with sharp spinules, alter- 

 nating on the two sides. Color of middle segments sabnon, thickly 

 specked with orange-brown and reticulated with red blood-vessels; 

 anterior and posterior segments greenish or yellowish white. 



Off Cape Cod, 20 to 50 fathoms, in hard sand; tubes attached to 

 valves of dead bivalves (U. S. Fish Commission, 1879). 



Notomastus gracilis, sp. no v. 



Very small and slender. Head moderately acute in extension. Six 

 anterior segments bear fascicles of capillary set® above and below ; the 

 seventh and succeeding segments bear uncini above and below, but in 

 the lower fascicles of the seventh segment there are often some capillary 

 setee also. The fascicles are all small. The uncini are elongated, dis- 

 tinctly constricted toward the end, and expanded in a blade-like form 

 beyond, with the tip only slightly hooked. Color red. Length, ^0""" or 

 more; diameter, 0.05""". 



Noank, Conn., 4 to 5 fathoms, mud (U. S. Fish Commission, 1874). 



This species resembles N'. filiformis Verrill, but differs in the form and 

 arrangement of the setae. In the latter, the five anterior segments bear 

 large groups of long, capillary, acute setae; but on the fifth there are 

 sometimes a few uncini mingled with the capillary ones in the lower fas- 

 cicles. The uncini are numerous on the following segments, and are 

 long and somewhat bent, but show no constriction, the distal portion 

 being regularly narrow, spatulate, or paddle- shaped, with the central 

 shaft curved, blunt, and slightly hooked at the tip. In some specimens 

 there are two well marked black eyes. The tip of the head is elongated 

 and acute. 



The genus Aneistria Quatrefages would include both the above spe- 

 cies, but it seems to be impossible to distinguish that genus by any defi- 



