58 ON THE ECHINODERMATA OF THE 



Between the tentacle-scales of these first five or six tentacles and the generative slit, 

 there are occasionally one or two spinules. 



Towards the mid arm, the side arm-plates are tumid at the sides, nearly flat below, 

 broader than long, and shortest where they are joined longitudinally. They have a 

 sharp bend to reach the side of the arm, and terminate above in an angular edge by 

 joining the outer edges of two upper arm-plates. Their distal margin, at the side of the 

 arm, is thick, and supports two very small, distant, irregular, sharp, short spines 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. Some- 

 times 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 convex 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, however, being curved irregularly. 



Remarks. Two specimens of this fine Ophiuroid were collected 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-papilla?, 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 Ophio- 

 glyphan affinities as a whole, are very characteristic. The absence of spined generative 

 and radial scales, and the presence of tooth-papillae, separate the new forms from Ophio- 

 glypha ; and the nature of the dental apparatus and tentacle-scales prevents their being 

 placed in any hitherto known arctic genus, except OpMopleura. 



The specimens were dredged in Discovery Bay at a depth of 25 fathoms, the 

 temperature being 29'5. The species has since been found in high latitudes on the 

 eastern side of Greenland. 



OpMopleura borealis, Danielssen & Koren, was not found very far north, and only 

 in latitude 63 5' N., and to the east of Greenland ; but the specimens were from 

 considerable depths, 510 to 570 fathoms, and the bottom temperature was above 



