852 PROCEEDINGS OF THE ACADEMY OF [DeC, 



equal and well distinguished on the ventral side, but thin-walled and 

 coalesced dorsally. The ventral body walls between the tori are well 

 provided with glands forming indistinct ventral plates on each segment. 

 On the first four thoracic segments the flange-like ridges above the 

 setse are very distinct and, together with the pectinated membrane on 

 somite V, bound a quadrate area in which the branchiae arise. Anterior 

 to the gills this region is marked by several slight transverse furrows. 

 The postbranchial membrane is thin and deep and closely appressed to 

 the dorsum of the thorax. It springs from the anterior border of V, 

 and reaches nearly to the anterior border of IV, the free border being 

 provided with eighteen blunt but prominent teeth. 



The four pairs of branchiae are permanently bent forward over the 

 prostomium, and each has a length slightly exceeding twice the width 

 of the thorax. They are all rather thick and coarse and taper from 

 above the base to the bluntly pointed tip. For the basal one-fourth or 

 one-fifth they are constricted and those on each side coalesced and so 

 arranged that three lie externally, apparently arising from II, III and 

 IV, and one internally on somite III. Between the latter, and uniting 

 them across the middle line, is a thin membrane. 



Somites II, III and IV bear short oblique lines of small setae on the 

 highest part of the lateral ridge, on the medial side of which and just 

 posterior and lateral to the branchiae, there is on each side of III a 

 single very large claw-like spine. On V and all succeeding thoracic som- 

 ites the setae are in small tufts borne on truncate papilla? having the 

 usual position. Each tuft contains about eleven or twelve setse in two 

 rows. Thoracic tori are constricted at the base, broad, truncate and 

 beveled at the end. The uncini are borne on the thickest portion of 

 the bevel, so that the free, thin margin projects a considerable distance 

 beyond them. On somite X there are 63 uncini. Abdominal tori are 

 narrow but much longer and of uniform width throughout, and the un- 

 cini are borne on the extreme unbeveled end. Somite XXV bears 36 

 uncini. The notopodial cirri are small and not conspicuously enlarged 

 distally. 



The setae are all arranged in two equal rows. Those in one are larger, 

 stouter and more broadly winged. Otherwise they are similar in both 

 rows, and all have the stems slightly curved and strongly striated with 

 the ends very acute and tapering. The isolated postbranchial spine is 

 large and stout and has exactly the form figured by Mcintosh for M. 

 cristata. 



The uncini (figs. 9 and 10) also resemble those of that species. Usu- 

 ally they have three teeth above the ligament process, but occasionally 



