76 



plates divided, on the middle line, into halves, which, at the base of 

 the arm, are placed at the outer lower corner of the joint, on each 

 side, being separated by a number of supplementary pieces. At the 

 tip of the arm the plate is simple ; then it divides in two, and the 

 halves are gradually forced apart by the intrusion of supplementary 

 pieces. Two short genital slits, extending only half-way to the 

 margin of the disc, and beginning outside the mouth-shields.* 



Ophioplocus tessellatus, Lyman. 



Special marks. Color gray, with obscure cross-bands on the arms. 

 Length of arms, in adults, four to five and a half times the diameter 

 of the disc. 



Description of a specimen. Diameter of disc 1 7 millim. Width of 

 arm, without spines, 3.5 millim. Length of arm 70 millim. Mouth- 

 papiUas five on each side, and one odd one, placed just under the 

 teeth ; the side papillas squarish, flat, and crowded ; the odd one 

 resembling the teeth. Teeth five, thick, short, stout, broader than 

 long, with a curved cutting edge. Mouth-shields broad heart-shape, 

 with a curve without and an angle within ; length to breadth, 1 : 1.5. 

 Side mouth-shields large and of even width, 5 millim. wide. Under 

 arm-plates squarish, very regular and clear in outline, shghtly sepa- 

 rated, thick; outer side curved, lateral sides a little re-enteringly 

 curved; length to breadth (10th plate) 1 : 1.3. The halves of the 

 upper arm-plates are rounded triangular, very much like the supple- 

 mentary pieces in Opkionereis ; at the base of the arm they lie very 

 low down, so that the side arm-plates are much reduced in size ; they 

 are separated from each other by six supplementary pieces, of which 

 one lies on the middle line of the arm, and the other five make a sort 

 of semicircle round it ; at the base of the arm the central piece of 

 this semicircle becomes very small indeed, and is often divided in 

 two ; between the supplementary pieces there are sometimes single 

 large grains. The halves of the upper arm-plates and the supple- 

 mentary pieces are thick and swelled, and often of about the same 

 size. Side arm-plates small and almost covered up by the arm-spines. 

 Scales of the disc a little larger above than below, mostly overlap- 

 ping, but with here and there a round scale ; varying somewhat in 

 size, the largest 8 millim. long. Kadial shields very small, about 1 

 millim. long, sunken in the scaling of the disc. Genital shts only 

 2 millim. long, starting 1 millim. outside the mouth-shield. Arm- 

 spines three, stout, round, blunt ; the lowest much the largest ; 

 lengths, to that of under arm-plate, .8, 1, 1.3 ; 1. Tentacle-scales two, 

 longer than broad, flat, nearly oval. Color, in alcohol, gray, with 



* Ophiolepis imbticata doubtless belongs to this genus, and may be considered the 

 type. 



