188 Prof. P. M. Duncan on Liitkenia, 



XXIII. — On Liitkenia, a new Oenus of Ophiuroidea from 

 Discovery Bay. By Prof. P. Martin Duncan, M.B. 

 Lend., F.R.S., &c. 



[Plate IX.] 



After the Echinodermata brought to England by the late 

 Arctic Expedition under the command of Sir George Nares, 

 F.R.S. &c., had been described by Mr. Percy Sladen and 

 myself*, a box of specimens, which had been collected by Mr. 

 Hart, naturalist to H.M.S. * Discovery,' was found unopened. 

 It was sent from the Koyal Society to the British Museum ; 

 and Dr. Giinther, F.R.S., very kindly placed the Echino- 

 derms in my hands. Mr. Edgar Smith, E.L.S., drew my 

 attention to the two fine specimens which form the subject of 

 this memoir ; and after dissecting one I found it desirable to 

 describe them under a new genus, which has very remarkable 

 peculiarities. 



Genus Lijtkenia. 



Disk notched, covered with very small scales. Radial 

 shields small, widely separate. Mouth-papillse numerous. 

 Tooth-papillai. Teeth resembling tooth-papilla3 in double 

 series, with accessory knobs. Generative slits small, midway 

 between mouth-shields and margin. Accessoiy scales to ten- 

 tacular openings ; tentacle- scales numerous ; on mid arm two. 

 Spines small, distant, irregular. Lower arm-plates very broad 

 and short within tlie disk, and small and triangular without. 

 Side arm-plates meeting below throughout, but not above. 

 Upper arm-plates broad and keeled near the disk. 



Liitkenia arcti'ca, sp. nov. 



The disk is large, subcircular in outline, tumid above and 

 at the sides, flat below, and is notched over the arms (ly^y inch 

 in diameter). 



Tlie arms are twice and a half as long as the disk is 

 broad, come well within it, are very broad within the disk, 

 and considerably so until the second third of their length. 

 They are flat beneath, convex and almost keeled above near 

 the disk, and less so distally, tall at the sides, and generally 

 triangular in outline. The arm-spines are very small and 

 few in number. The colour is white with a little brown. 



The upper surface of the disk and the interbrachial spaces, 

 to the aboral edge of the mouth-shields, and except the 



* Ann. & Mag-. Nat. Hist. 1877, vol. xx. p. 449. 



