No. IX. ECHINODERMATA. 273 



than broad ; length less than, or only equal to, their distance 

 from the margin of the disk. Papillae of the disk-incision 

 about fifteen, and rather broad. Under arm-plates widely 

 separate, of a very broad, short triangle-shape. Two tentacle- 

 scales. No infrabrachial indentations. Spines rather long, 

 equal in length to the side arm-plates. 



This is the most northerly echinoderm brought home by the 

 Expedition, a fine specimen with a disk-diameter of 26 millims. 

 having been taken by Capt. Feilden at the winter-quarters 

 of H.M.S. ' Alert,' in N. lat. 82 27'. Other examples of 

 this species were obtained at Discovery Bay, and among 

 them one which is provided with remarkably long arm-spines, 

 being in relative proportion fully twice the length of the 

 spines generally occurring in 0. Sarsii. In this individual 

 the three spines of the sixth joint measure respectively 2*45 

 millims., 2*25 millims., 1'4 millim. ; the under arm-plate 

 being *7 millim. long, the arm-joint 1 millim., and the disk- 

 diameter 15 millims. The remaining features of the specimen 

 agree too closely with the characters of 0. Sarsii (Liitk.), Lym., 

 to warrant its removal, in our opinion, from that species, even 

 as a provisional variety. 



In some cases great irregularity is exhibited in the mouth- 

 papillae, one abnormal example being particularly worthy of 

 notice. In the Ophioglyphce the innermost mouth-papilla 

 generally stands immediately over the teeth, and might be 

 easily mistaken for a tooth, being, in fact, affixed to the tooth- 

 plate and not to the lateral plates. In 0. Sarsii, as well as 

 in other members of* the genus, two additional papillae are 

 generally associated with it, one on either hand, and are in 

 like manner borne by the ossicle upon which the teeth are 

 placed. 



In consequence of this arrangement it has long seemed 

 probable to one of us that these subdental papillae should be 

 regarded as tooth-papillae (of which they are in truth the 

 homologues) rather than as mouth-papillae, so-called, along 

 with which they are commonly counted. One of the speci- 



VOL. II. T 



