17 



knobs, similar in form to those of the marginal plates, 

 but smaller. 



The long, narrow mouth-plates carry a double row 

 of little, short and compressed papillae, the largest spec- 

 imen having about 20 in each row. The first adam- 

 bulacral plate has a double raw of papillae with 12 papilla; 

 in each row. The 2nd has 6 papillae, the innermost of 

 which is larger and more compressed than the rest, 

 and resembles the large compressed middle papilla of 

 the other adambulacral plates. These plates have 5—6 

 papillae the middle one of which was larger as well as 

 more slender and compressed than the rest and reached 

 into the ambulacral furrow. Verrill ') writes :— "The pecu- 

 liar purselike or bursiform pedicellariae of the large inner 

 adambulacral spines, characteristic of Bathybiaster, are 

 often entirely wanting in our specimens, especially when 

 small, and usually, when present, there are but few of 

 them even in the large specimens. Possibly they may 

 have been destroyed by rough usage in the dredges and 

 washing sieves". An examination of the "Michael Sars's" 

 specimens shows that this "purselike or bursiform pedicel- 

 laria" is identical with the "vexillum" of Bathybiaster 

 vexillifer, which as demonstrated by Mortensen 2 ) is no 

 other than the middle papilla of the adambulacral plates, 

 and as such it was described by me above. It is similar in 

 form to the papilla in Bathybiaster vexillifer, but appears 

 to be somewhat shorter and broader. It is often lost 

 as already stated by Verrill, and was entirely wanting in 

 some of the specimens examined by me; in others it was 

 present in a few of the adambulacral plates only, and 

 merely in a very few specimen it was found in all the 

 plates. 



Bathybiaster vexillifer Wyville Thomson. 

 Archaster vexilifer Wyville Thomson, The Depth of the Sea, 1873, 

 p. 150, fig. 25. 



9 /s— 10 /s. Stat. 102, 60 57' N, 4°38'W, 1098 m., dark sand and 

 clay, temp. 0.9° Cel. 24 specimens. The smallest specimen measu- 

 red: arm-radius 52mm., disc-radius 11 mm., the largest: 106 mm. and 

 21 mm. respectively. 



Bathybiaster vexillifer was discovered by the "Porcu- 

 pine" in 1869 in the cold area of Faroe— Shetland Channel 

 (stat. 76, 60° 36' N, 3° 58' W, 630 m., temp. -5- 1.1° Cel.) It 

 was found subsequently at a number of localities in 

 the cold area of the Norwegian Sea (the „Yoeringen", 753 — 

 2222 m., temp. -:- 1 to -s- 1.6°, the "Michael Sars", 600— 

 1960 m., temp. -5-0.41° to 1.07°, the "Armauer Hansen", 

 1400 m. temp. -~ 0.74°, the "Thor", 877—1401 m., temp, 

 -h 0.58 to -s- 0.95°, the "Princesse Alice", 1185—1865 m. 



') Proc. U. S. Nat. Museum, vol. 17, 1894, p. 256. 

 2 ) Mortensen: Echinoderms, Danmark Exp. Gronlands Nordost- 

 kyst 1906-1908, Bd. 5 no. 4, 1910, p. 252. 



and the "Danmark", 304m.) It was likewise found by Swedish 

 expeditions in the cold area of the Norwegian Sea, but 

 no reference to the individual localities was given. Bathy- 

 biaster vexillifer is thus distributed in the Norwegian 

 Sea between 60° 36' and 79 ' 59' N. and between 14 J 24' 

 E., and 18 J 30' W. in 304-2222 m.and in temp. : 0.41 to 

 -f- 1.6 ' Cel. It is besides found off western Greenland 

 between 64 J 5' and 70' 47' N., 223-1276 m. 



Bathybiaster robustus was taken by the "Challenger" 

 at three localities off the east coast of North America, 

 2269—3111 m., temp. 2.33-2.89". It was likewise taken 

 there by American expeditions in several localities between 

 35° 10' and 41° 28' N., 1290— 2665 m. All the stations 

 belong to the warm area, as, according to the records 

 of the cruises of the "Albatross" in 1883 and 1884, the 

 temperatures ranged between 2.78 and 3.89° at the depths 

 at which B. robustus was found. B. robustus was not 

 hitherto known to occur on the east side of the Atlantic. 

 The stations off Ireland and the Hebrides also belong to 

 the warm area. This species is therefore a pronounced 

 warm-water form restricted to the depths of the North 

 Atlantic, 1290- 3110 m. while the closely related B. vexil- 

 lifer, as shown above, is a true Arctic species. 



Verrill remarks about these two closely related forms, 

 "that they may prove to be indentical when a full series 

 of each can be compared", and Koehler 1 ) joins him in 

 this view, as he considers B. robustus and its synonym 

 Phoxaster pumilus Sladen 2 ) identical with B. vexillifer" . 

 The two species, as I have stated before, however, have 

 their distinct habitats, the one being restricted to the 

 warm area of the Atlantic, the other to the cold area 

 of the Norwegian Sea and the waters off the west coast 

 of Greenland where the hydrographic conditions are 

 probably also Arctic. Neither reaches the banks, that 

 divide the Norwegian Sea from the Atlantic. This dif- 

 ference in distribution indicates that the species must be 

 distinct and a closer examinations of their structure con- 

 firms this view. 



In B. robustus the marginal plates have a more 

 vertical position than in B. vexilifer, where the arms do 

 not exhibit the rectangular straightened appearance seen in 

 the former species. B. robustus has 1 to 2 spines on 

 the dorso-marginal plates and 2 to 3, or more rarely 4, 

 on the ventro-marginal ones. In B. vexillifer the dorso- 

 marginal plate bear to 1 in exceptional cases 2 spines ; 

 the ventro-marginal plates on the other hand, 1 or 2 

 very rarely 3 or 4 spines. In the first-named species 

 the spines are larger than in in the other, and the 



') Koehler; Echinodermes, Res. Camp. Sci. Monaco, Fasc. 34, 

 1909, p. 57. 



2 ) Sladen: Challenger Asteroidea, p. 336, tab. 15, figs. 3 — 6, 

 tab. 40, figs. 7—10. 



GRIEG ;-ECHINOD. - 3 



