OPHIURA PANAMENSIS. 33 



breadth, 1.5 : 1.3. Arm-spines ten, rounded, little tapering, little flat- 

 tened, decidedly stout ; of nearly equal length, except the two lowest ; 

 lengths uf uppermost and of the lowest to that of under arm-plate (thir- 

 teenth joint), .S, 1.1 : 1.4. Near the ti]) of the arm, the spines are six in 

 numher, and more rounded and slender. Tentacle-scales large ; inside 

 one long, regular oval; outside one unusually broad. Color, in alcohol: 

 above, greenish gray, with a white mark in the cx'ntre ; arms banded 

 with lighter and darker greenish-gray ; under surface uniform light 

 greenish-gray. 



Variafionfi. — The color varies in intensity, sometimes being clouded 

 with brownish, and again tending to light greenish ; the central white 

 spot, though common, is not always found. The young of this species 

 have no radial shields ; one, with a disk of 7""°', was just beginning to 

 show them; while another, with a disk of 11"""-, was still entirely granu- 

 lated. This case is just reversed in 0. feres. A specimen with a disk 

 of G.-j™""' had already eighteen mouth-papilla), but only seven arm-spines. 

 The proportions of the disk to the arms w^ere as follows, in different 

 specimens : 26 : 96, 21 : 70, 20 : 75, 14 : 46, 13 : 52, 9.5 : 40, 6.5 : 23 ; so 

 that the disk is usually contained m the arms from three and a half to 

 four times. 



This species differs from others with unequal arm-spines and with 

 radial shields, as follows : from 0. cinerea and 0. squamosissima, in 

 having the upper arm-plates undivided ; from 0. rubiciinda, in the dif- 

 ferent shape and position of the mouth-shields. 



I am not quite sure that this is the true Ophioderma panamensis Ltk. 

 Dr. Liitken got his specimen from the Smithsonian Institution. There 

 are now at the Smithsonian Institution and at the Museum of Compara- 

 tive Zoology many specimens of the Ophhira here described ; besides 

 which there is a single specimen (1181 Smithson. Instit.) which may be 

 the same species, or a variety ; the arm-spines are sharper, a little, and 

 there are dark, longitudinal lines on the outer edges of the upper ann- 

 plates. Neither of these agrees perfectly with Liitken's description ; 

 the differences consisting in slight variations in the spines, and in the 

 markings of the upper arm-plates ; still, they are all probably the same, 

 and are therefore here included under 0. panamensis. 



