196 PROCEEDINGS OF THE ACADEMY OF [Vol. LXXV 



4339, same locality, 241-369 fathoms, green mud, (type); 4402, 

 off San Clement e Island, 542-599 fathoms, green mud; 4406, off 

 Santa Catalina Island, 650 fathoms, green mud; 4436, off San 

 Miguel Island, 264-271 fathoms, green mud, 2 specimens; 4487, 

 off Santa Cruz Lighthouse, 18-19 fathoms, hard gray sand. 

 Pista brevibranchiata Chamberlin. 

 '-/ A Species well represented by upwards of forty specimens and 

 which was described in the original manuscript under the name of 

 P. fimhriata appears to be this species. It belongs to the Scionopsis 

 group, having aboreseent instead of bottle-brush-like gills. 



If this identification is correct, Chamberlin 's single example is 

 not in all respects typical. 



Characteristics of the species are the wings and frills which 

 adorn somites I to VII and the form and close approximation of 

 the gills. Typically there are two pairs of gills, but they are always 

 asymmetrical and seldom more than two are well developed. Any 

 one, two, or even three, may be wanting but usually three gills are 

 present, in which case the two best developed are usually placed 

 diagonally and the third is much smaller, very simply branched, 

 or even cirriform. When fully developed, the gills consist of a 

 thick, columnar stem bearing at the top from three to five branches 

 arising at the same level and spreading horizontally. Between 

 these there may be a few small secondary branches. The large 

 branches dichotomize unequally three or four or even six times to 

 form the delicate terminal filaments. In a few cases one or two 

 smaller branches arise from the main stem at a slightly lower level 

 than the main branches as though secondary divisions of these had 

 become independent. 



Pairs of small papilliform cirri occur on the dorsum of V, VI, 

 and VII. Those on III lie close to the furrow III/IV and are 

 non-retractile; those on VI and VII lie above and behind the corres- 

 ponding setae tufts and arise out of small pits into which they appear 

 to be retractile. 



The uncini resemble Chamberlin 's figure except that the sinus 

 between the beak and the neck is broader and the guard, instead 

 of being incomplete, is very long and reaches to the apex of the 

 beak but is very delicate. They form a single series from V to X 

 inclusive and on abdominal tori and double interlocking series on 

 XI to XX inclusive. They are large and with well-developed 

 manubrium to X, behind which they become gradually reduced 

 in size and the handle more slender and weaker until it disappears. 



Stations 4339, off Point Loma Lighthouse, 241-369 fathoms, 

 green mud; 4364, same locality, 101-129 fathoms, green mud; 4430, 

 off Santa Cruz Island, 197-281 fathoms, black sand and pebbles; 



