REPORT ON THE OPHIUROIDEA. 205 



A smaller specimen with a disk of 10 mm. varied little, except that the upper arm 

 plates were narrower and thinner, and the disk scales smaller and beset with few spines. 

 This species differs from Ophiomitra plicata in the cloven or thorny tentacle scales, and 

 in the greater number of arm spines. 



Station 146.— December 29, 1873 ; lat. 46° 46' S., long. 45° 31' E. ; 1375 fathoms; 

 globigerina ooze. 



Ophiomitra chelys, Lym., Bull. Mus. Comp. Zool., vol. v., part 7, p. 152, pi. ix. figs. 

 239-241, 1878 ; Bull. Mus. Comp. Zool., vol. v., part 9, p. 231. 



Ophiacantha chelys, Wyv. Thorn., Voyage of the " Challenger," Atlantic, vol. ii. p. 64, figs. 16, 17. 



Radial shields widely separated ; along their entire interbrachial margin run large disk 

 plates. Under arm plates not swollen. Tentacle scales large and fiat. Under arm spine 

 thickened and curved. 



(Type specimen from Station 84.) Diameter of disk 9 mm. Length of arm about 

 85 mm. Width of arm near base 2*8 mm. Mouth pap illse usually eleven to each angle, 

 of which the central one within is wide and flat ; the next three on either side are stout 

 and pointed, and the outer ones are irregular, compressed, and sometimes broken. Teeth 

 similar in shape to the odd innermost mouth papilla. 1 Mouth shields small, as long as 

 broad, shield shaped, with a well-marked obtuse angle inward and outer margin sometimes 

 turned down ; length to breadth, 2 : 2 - 3. Side mouth shields broad and thick, a little 

 widest at outer ends. Under arm plates large, thick, and regular, much wider than long, 

 reaching at their outer edge entirely across the arm ; cleanly curved without, re-enteringly 

 curved on sides, and having a little peak within where separated from next plate. First 

 plate small, narrow wedge shaped. Upper arm plates somewhat swollen, widely separated, 

 wider than long, bounded without by a gentle curve, and within by an obtuse angle or a 

 deep curve. Side arm plates prominent and meeting freely above and below. Disk thick 

 and rising well above the arms, with a very deep, narrow constriction and furrow in each 

 interbrachial space. The space between this furrow and the radial shields is on either 

 side occupied by four large plates running diagonally inward, whereof one or more are often 

 broken in two. The central disk is sunken, and covered by small, coarse, irregular scales, 

 which, with the larger plates, are sparsely beset with short, blunt, usually smooth stumps 

 or spines, which form also an irregular clump over each arm. Radial shields deejay sunken 

 in a furrow, widely separated by a high ridge of irregular scales, much longer than broad, 

 presenting an acute angle inward ; length to breadth, 3 : "8. Near base of arm six stout, 

 very thorny, glassy, blunt, cylindrical arm spines, the lowest ones much the stoutest ; 

 lengths to that of an arm joint, 3"6, 3"6, 2 - 8, 1"7, V7, 1*7 : 1*2. Two-thirds out on the 



1 The nomenclature of the various papillae of the mouth is of course conventional. In most cases the lowest 

 tooth may also be called the innermost mouth papilla 



(zool. chall. exp. — part xiv. — 1882.) 27 



