192 Prof. P. M. Duncan on Lutkenia. 



and two tentacle-scales, the inner of which is small and scale- 

 like ; and the outer is usually, but not invariably, a minute 

 spine longer than the scale and the other spines. Sometimes 

 the two tentacle-scales are equal, and further out the largest 

 spine becomes independent of the tentacle. There are often 

 no spines, while some plates have several very minute ones. 

 All are very ill-developed and small. 



The side arm-plates form the bulk of the tip of the arm ; 

 but although convex at the sides and swollen above, they do 

 not separate the small and somewhat elongated hexagonal 

 upper arm-plates there. 



The upper arm-plates, within the notch in the disk, are four 

 in number, and are broad, short, and curved to form a convex 

 roof-like surface. Until far out on the arm, all are much 

 broader than long, and have slanting straight sides and very 

 faintly curved distal and proximal margins ; the plates are con- 

 vex and angular longitudinally, and they form the upper and 

 much of the side arm. A little beyond the mid arm the upper 

 arm-plates are smaller, not much broader than long, broadest 

 without, where they are curved; and further out they are 

 longer than broad, narrow proximally, with sides reenteringly 

 curved and the distal margin boldly curved without. Towards 

 the tip the elongated hexagonal form is assumed, the distal 

 edge being, however, curved irregularly. 



Remarks. — Two specimens of this fine Ophiuroid were col- 

 lected by Mr. Hart : one is in spirit, and the other is dry, in the 

 British Museum ; and they both have the same anatomical 

 details. 



The minutely scaled disk, the widely separated radial shields 

 and their free aboral edge, the position and ornamentation of 

 the generative slit, the presence of mouth- and tooth-papillte, 

 the absence of true teeth in the ordinary sense, the papillose 

 nature of the jaws, the accessory scales to the tentacular 

 openings, the shape of the lower arm-plates, the numerous 

 tentacle-scales and few spines on the side arm-plates, and the 

 angular roof-shaped upper arm-plates, whilst they partly 

 suggest Amphiuran and Ophioglyphan affinities as a whole, 

 cannot admit the forms under any described genus. The 

 absence of spined generative and radial scales and the 

 presence of tooth-papillse separate the new forms from 

 OjjMoglypha ; and the nature of the dental apparatus and ten- 

 tacle-scales prevents their being placed in any hitherto 

 known arctic genus. 



There is, then, an evident necessity for the foundation of a 

 new genus, as these forms are unlike any others. I have 

 named it after Prof. Liitken. 



