1923] NATURAL SCIENCES OF PHILADELPHIA 205 



but owing to the form of the ])arai)0(lia more or less strongly- 

 quadrate in section, especially toward the caudal end. Pygidium 

 a short, simple ring with large anus and a pair of slender, tapered, 

 ventro-lateral cirri which vary in length from 1| to 3 times the 

 diameter of the pygidium, according to the state of extension. 



Branchial fold low but broad, connected at the sides anteriorly 

 with the paleolar tul)ercles, anterior margin deeply concave, 

 arching over III and roofing a recess. Interbranchial area keystone- 

 shaped with an anterior median notch, very little longer than wide, 

 less than the branchial fold and not reaching to posterior border 

 of V. The lateral border of this region is marked by a deep groove 

 which passes between the paleolar tubercle and the setigerous 

 tubercle of IV, being, therefore, the boundary between these two 

 somites. It is unequally conspicuous in different specimens. 

 Branchial scars large, slightly elevated on branchiophores, ar- 

 ranged in a crowded lozenge-shaped figure, the two anterior pairs 

 on IV and united by a fold of integument with the paleolar tubercle, 

 the two posterior on V, but the more laterad connected with \1 also. 



Gills easily detached, large, nearly half length of thorax, stout 

 at base, regularly tapered to acute tips, terete or nearly so, sometime 

 more or less coiled, marked with fine transverse furrows which 

 become more conspicuous in contraction. 



Parapodium III bears paleolar tubercles only; IV, V, and VI 

 setigerous tubercles only, the remaining thoracic somites ]>oth 

 tubercles and uncinigerous tori. Setigerous tubercles are prominent, 

 slightly compressed, cylindroid, rising o])liquely from the parapodial 

 flange or ridge; distally divided into two low lips between which 

 the setae arise in a slightly curved rank, at the ventral margin of 

 which is the short clavate cirrus. The tubercles on IV and \' are 

 much smaller than the others and bear larger, much more thickened 

 cirri, that on IV crowded beneath the one on V. Uncinigerous 

 tori begin on VII ventral to the parapodial ridge as auricular 

 lappets with contracted base and long free margin just l)chind 

 which the long rank of uncini is borne; dorsal and ventral angles, 

 especially the latter, produced. Anteriorly the uncinigerous margin 

 is about as long as the segment but posteriorly gradually becomes 

 shorter and the tori more elevated and with less contracted base. 

 On abdominal segments the tori are narrower and longer with 

 shorter uncinial line. These characters become more pronounced 

 posteriorly until the last torus is almost stalk-like and projects 

 beyond the anus along with the caudal cirri. All of the posterior 

 tori bear a minute cirriform process at the dorsal end of the line 

 of uncini. True dorsal cirri are large, flat, bent processes shaped 

 like the paddles of swimming crabs and well separated from the 

 uncinigerous tori with whicli they are connected by thickenings 

 resembling the l^roken parapodial ridge. Posteriorly the gaji widens 

 until it equals the depth of the segment, the torus being at the 



