334 bulletin: museum of comparative zoology. 



of disk. Oral papillae about 10 on a side the penultimate (distally) 

 distinctly the largest. First under arm-plate, small, somewhat tri- 

 angular, wider than long; second plate tetragonal or somewhat 

 pentagonal, longer than wide, distal corners rounded; succeeding 

 plates tetragonal or slightly hexagonal, about as wide as long, distal 

 corners much rounded; far out on arm, the plates become distinctly 

 longer than wide; they are broadly in contact throughout. Side 

 arm-plates low and small, confined to sides of arm; each carries a 

 series of 9 (rarely 10), flat, blunt arm-spines, closely appressed to arm; 

 the lowest is bluntest and longest but is not equal to the arm-segment; 

 the others are successively shorter and less blunt to the uppermost 

 which is bluntly pointed and scarcely half as long as the segment. 

 Tentacle-scales 2, the outer short, wide, truncate, and overlapping 

 the base of the lowest arm-spine; the inner longer, narrower, and 

 rounded at tip. Color, in life, disk deep red above and below; arms, 

 above deep green, below pale reddish proximally but becoming pale 

 greenish distally; arm-spines, reddish or dull orange with conspicu- 

 ously lighter tips. 



The above description is that of a typical specimen but there is 

 much individual diversity in certain particulars. The smallest 

 specimen found has the disk 15 mm. across; in the largest it is 23 mm. 

 In the smallest specimen and in most of the others all of the radial 

 shields are bare and of approximately equal size, but in several speci- 

 mens, one or more of the shields are concealed by the granules; in 

 a specimen 16 mm. across the disk, only one radial shield is visible. 

 The number of arm-spines is surprisingly constant; not one case of 

 eleven spines has been seen and in no specimen does the number fall 

 short of nine; but there is much diversity in the size and shape of the 

 spines, for they are often shorter, thicker, and more pointed than in 

 the holotype, while occasionally they are slightly longer. The most 

 notable diversity shown by this series of specimens is in color. The 

 majority have the characteristic red disk and green arms, with light- 

 tipped arm-spines, but at one extreme is a specimen almost uniformly 

 green (seen from above) while at the other is a red specimen that shows 

 no trace of green. The typical specimens had the red of the disk, 

 in life, what Ridgway (1912) calls nopal red (midway between no. 26 

 and 27 of Klincksieck and Valette, 1908), while the arms ranged from 

 Ridgway 's dark citrine (K. & V. 179-180) through spinach-green 

 (K. & V. 304-305) to bright meadow-green (K. & V. 326-327). In 

 some specimens with otherwise wholly red disks, the oral shields are 

 dusky greenish, but in all the specimens seen, the jaw-angles proximal 



