166 PROCEEDINGS OF THE ACADEMY OF [Jan., 



mm. There are eight setigerous thoracic and twenty-five abdominal 

 somites. The thoracic and most of the abdominal somites are ob- 

 scm-ely equally biannulate. Ventral i3lates are confined to the thoracic 

 segments and are divided into two equal parts by the transverse inter- 

 annular furrows. The last eight abdominal somites are more distinctly 

 differentiated, and decrease rapidly in diameter to the short rounded 

 pygidimn. From them the broad caudal membrane arises just ventrad 

 of the setffi, continuing anteriorly around the ventral surface nearly to 

 the middle hne, but posteriorly spreading widely as a horizontal plate 

 with a median emargination in which the pygidium lies. The basal 

 part of the membrane exhibits distinct metameric thickenings which 

 disappear toward the margins. 



The anus is situated slightly ventrad in a small slit, from which the 

 very faint fsecal groove passes forward between the ventral cleft of 

 the caudal membrane to the posterior margin of somite IX, where 

 it turns to the left, passes obliquely across the side of this somite and 

 disappears in front of the setigerous area, but reappears in the dorsal 

 middle line of VIII and continues to the peristomium, where it turns 

 slightly to the left and disappears finally on the collar. 



The collar is ver}^ peculiar. It is thin and rather high, its margin 

 even all around, but, owing to the obliquity of the peristomium due 

 to the prolongation forward of its ventral plate, the height of the collar 

 appears to be about twice as great dorsally as ventrally. The median 

 ventral part is injured so that the character of the ventral lobes cannot 

 be ascertained. Laterally at the level of the sides of the ventral plates 

 is an abrupt thinning, folded in the form of a little niche terminating 

 at the base in a minute pit; but there is no actual incision. Dorsally 

 a somewhat similar condition exists, each half of the collar being ad- 

 herent to the median line by a very delicate membranous fold, so that 

 no actual cleft is present, The fold of the right side overlaps the left 

 broadly, and thus deflects the end of the feecal groove toward the 

 latter side. No eyes nor otocysts are visible on either the peristomium 

 or pygidium. 



As indicated by the measurements the branchice are relatively 

 elongated, contributing about ^ of the total length. The basal lobes 

 are exceedingly short and are entirel}^ concealed Avithin the collar. 

 There are 15 branchial radioles on each side, arranged strictly in one 

 row and of equal length. They show no tendency to coil or twist. 

 The radioles of each half are connected for ^ of their length by a delicate 

 membrane, to which they stand in the relation of the ribs to the cover 

 of an umbrella, and which is continued as a delicate wing, especially 



