MUSEUM OF COMPARATIVE ZOOLOGY. 227 



skin, sparsely set above with short, slender, rounded spines, about 1.2 mm. 

 long. Arm-spines three ; the two lowest slender, rounded, pointed, often 

 bent, and in length about 1.5 mm. On every second or fourth joint, and on 

 alternating sides, the upper spine is much thickened, and has the clove-shape 

 characteristic of the genus ; its length is about 2.5 mm. Towards the end 

 of arm there are no such spines, but the upper one is usually the longest and 

 stoutest. No tentacle-scale ; the tentacles are rather long and thick and 

 without papillae. Color, in alcohol, disk dull greenish brown ; arms yellow- 

 ish brown. 



Philippines ; C. Semper. 



Ophioplocus Esmarki sp. nov. 



Plate V., Figs. 12 - 14 ; Plate VI., Fig, 6. 



Special Marks. — Color, in alcohol, uniform dull purplish above, and light 

 brown below. Arms decidedly flattened, having the width to the height 

 3.5 : 2. Arm-spines not tapering, and of nearly equal length. 



Description of a Specimen. — Diameter of disk 16 mm. Length of arm 

 53 mm. Width of arm 3.5 mm. Distance from outer side of mouth-shield to 

 inner point of teeth, to that between outer corners of mouth-slits, 3 : 3.2. 

 Mouth-papillae five on each side, or rarely six, stout, irregular, or squarish; 

 the two outer ones rest on the side mouth-shield, the others on the mouth- 

 frames. Teeth five or six, the upper ones short, stout, broader than long, 

 with a curved cutting edge ; the lowest one smaller, nearly on a level with 

 mouth-papilla?, and resembling them. Mouth-shields heart-shaped, with a 

 curve without and an angle within; length to breadth 1.2 : 1.2. Side 

 mouth-shields long triangular, somewhat swelled, not quite meeting within ; 

 length to breadth 1.3 : 1. Under arm-plates broad pentagonal, with the odd 

 angle inward; length to breadth, close to disk, 1 : 1.5. The upper arm- 

 plate is simple only at the tip joint of the arm ; at the next joint a longitudi- 

 nal crease of division appears ; at the next the upper arm-plate is completely 

 divided, and there appear two supplementary pieces on the median line, of 

 which the outer one partly separates the- two halves of the plate. Farther 

 down the arm the two halves are wedged apart by the supplementary pieces, 

 whose number has increased to six or seven. Close to the disk most of the 

 upper surface is occupied by thirteen supplementary pieces, of which three, 

 of an irregular hexagonal form, lie on the median line. This development 

 of pieces is quite as in O. imbricatus. Side arm-plates small, and crowded 

 mostly to the under side of the arm. Scales of disk, above, irregularly im- 

 bricated and thickened; the longest 1 mm. long; below they are thinner, 

 finer, and more regular. Along edge of disk run half a dozen larger 

 rounded, swelled scales. Radial shields small, about 2 mm. long. Genital 



