228 PROF. F. JEFFREY BELL ON [A-P^- 7, 



3. Observations on a rare Starfish, BathyUaster vexillifer. 

 By F. Jeffrey Bell, M.A., Sec. E.M.S. 



[Eeceived Marcli 18, 1891.] 

 (Plates XXIII. & XXIV.) 



Among much valuable material received last year by Dr. Giinther 

 from Mr. John Murray there was a specimen marked " Archaster 

 vexillifer, Wyv. T. (unique)." This is, I doubt not, the type of the 

 species shortly described by the late Professor Sir Wyville Thomson 

 in his popularly written narrative of the cruises of the ' Porcupine.'^ 



This specimen, unfortunately, never came into the hands of Mr. 

 W. Percy Sladen, who has given us ample details as to the Starfishes 

 collected by the ' Challenger,' and as to most of those obtained by 

 earlier and later deep-sea expeditions. 



Messrs.. Koren and Danielssen, the acute and talented describers 

 of the Starfishes of the Norwegian North-Sea Expedition, when 

 instituting 2 a new genus for the form which they first called 

 Astropeeten pallidus, suggested that Thomson's Archaster vexillifer 

 should hkewise be placed under Bntliybiaster, and to this suggestion 

 Mr. Sladen has assented. 



The rarity and interest of species of this group justifies, I think, 

 a detailed account of Thomson's unique specimen, but that account 

 cannot, unfortunately, be made as complete as it should, for the 

 specimen has been dried. 



General Form. — The species is, obviously, flattened, but in the 

 drying the arms have been, unequally, drawn up so that the tips now 

 point upwards, and the dorsal surface is more or less concave. The 

 arms are very regularly triangular, 18'5 mm. wide at the base, and 

 gradually and regularly tapering to a fine point ; they are about 

 87 mm. long from the centre of the disc, the radius of which is 

 18 mm. The angle between the arms is rather sharp. The sides of 

 the arms are straight and high at the base, where they measure as 

 much as 12 mm. ; the diminution in depth of the arms is brought 

 about very gradually. The sides of the arms have a very stout 

 appearance. 



Ambulacra. — Wyville Thomson was fully justified in drawing 

 attention to the remarkable width of the ambulacra, for they are 

 nearly (8 mm. at the widest) half the whole width (17 mm.) of the 

 arm, near the base, and this relation of groove to bounding plates is 

 retained till quite near the tip of the arm. The proximate cause of 

 this great width is to be found in the relative position of the ambu- 

 lacral ossicles, which, instead of being set, as they ordinarily are, at 

 an angle to one another, are set side by side and in one and the same 

 plane ; the median groove is so extraordinarily shallow that one 

 cannot but be struck by the exposed condition of the ambulacral 



1 ' Depths of the Sea,' London, 1873, p. 160. 



^ Den Norske Nordhavs-Expedition, Zoologi— Asteroidea (1882), p. 89. 



