436 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



arms, is small, with the arms 60 mm. long, and the longest cirri 27 mm. long, wdth 24 

 segments. Another, still with 10 rays and 20 arms, is smaller, with the arms 45 mm. 

 long, and the cirri 25 mm. long, with 24 segments. There is another small specimen, 

 with 10 rays and 20 arms. The last specimen is very small, with 8 rays and 16 arms. 



Of the 3 specimens from Aurora station 3, two have 10 rays and 20 arms and one 

 has 9 rajs and 1 8 arms. 



Among the specimens from Aurora station 1 there are 32 with 10 rays and 20 arms. 

 One has 10 rays and 22 arms (as has also a specimen from station 12), two IIBr series 

 being present, abnormally developed (see p. 439), on the same IBr series. One speci- 

 men has 9 rays and 18 arms, and 2 small specimens have 6 rays and 12 arms. In a 

 specimen not quite full size the longest cirri are 70 mm. long, with 26 to 38 segments. 

 The terminal claw is sharp and very slender, gently curved in the pro.ximal third but 

 becoming straight in tlie distal two-thirds. In some of these specimens there is no 

 elevation at the synarthrial lines, while in others there are rather prominent small coni- 

 cal synarthrial tubercles. 



Among the 7 specimens from Aurora station 2, there are 4 with 10 rays and 20 

 arms, 2 with 9 raj'S and 18 arms, and 1 with 8 rays and 16 arms. A rather small speci- 

 men with 10 rays and 20 arms has the distal edge of the brachials everted and the dorsal 

 surface finely spinous. A specunen with 9 rays and 18 arms has the brachials with 

 the dorsal surface moderately roughened. A rather small and slender specimen with 

 10 rays and 20 arms about 140 mm. long is moderately rough. One of the specimens 

 with 10 rays and 20 arms is very small. 



From the Aurora collection without data there are 2 specimens with 10 rays and 

 20 arms. 



[Notes by A.M.C] The Discovery Investigations collection shows that the number 

 of cirri may exceed CC. Dr. Dilwyn John (1938) says that there is always a sharp con- 

 trast between the apical cirri and those of the more ventral part of the centrodorsal: 

 the latter are long, of up to 47 or, exceptionally, 65 segments; the former very much 

 shorter and of fewer segments. The contrast is greatest in large specimens; the longest 

 peripheral cirri may be three or more times as long as the shortest apical cirri. They 

 may be up to 130 nmi. long. 



P] may have as many as 75 segments and be up to 26 mm. long. The dorsal sur- 

 faces of the first 6 to 12 segments may be raised into thorny crests. P2 is usually of 

 fewer segments, five to ten less than in Pi, but in one Discovery specimen it has 62 

 segments. It is usually the same length as Pj. The first genital pinnule is normally 

 P3 or P<. P3 is commonly of 16 to 40, sometimes up to 60 segments. Whether it is an 

 oral or a genital pinnule it may be of roughly the same length as P2, but sometimes, when 

 it is a genital, it is very much shorter and of segments which decrease rapidly in stoutness 

 from the base to the end. P3 is usually of anj^thing from 5 to 20 segments fewer than 

 Pj of the same specimen; all but its basal segments are more elongated, being as much 

 as, or more than, twice as long as broad. The middle genital pinnides are of about 

 20 to 26, e.xceptionally more, segments; they are 10 to 20 mm. long, sometimes longer. 



Number oj arms. — Large specimens of this species almost invariably possess 10 

 rays and 20 arms, but rarely IIBr series resembling the IBr series are present and the 

 number of arms is increased to 22 or even 23. In small individuals the number of the 

 rays and arms is frequently reduced. 



