OPIIIOZONA IMPRESS A. 65 



Description of a Specimen. — Diameter of disk, 15.5"™'; from outer 

 side of inoutli-shield to outer corner of opposite mouth-slit, G™'"' ; 

 Avidtli of in-m ^vithout spines, 3.1""°; length of arm, G4"""- ; distance 

 from outer side of nioiitli-sliield to iniiei- ])oints of mouth-papilla?, to 

 that between outer corners of mouth-slits, 2.5 : 8.3. Mouth-pai)illa3 

 eleven ; outermost one slender, tapering, sharp, overlapping the next 

 to it, which is broader than long, and stout ; rest of papilla) short, 

 stout, pointed, somewhat rounded ; the whole form a close, even row. 

 Teeth five or six, regularly decreasing in width, from below upward ; 

 short, flat, regidar, Avith a curved cutting edge. Mouth-shields longer 

 than broad, bounded without by a long, ovoid curve, and within ]}y two 

 short lines, which are a little re-enteringly curved, and meet to form an 

 angle on the middle line ; length to breadth, 1.4 : 1. Madreporic shield 

 with a deep, round depression. Side mouth-shields thick, swollen, 

 slightly curved, having a little peak without, 

 running up to the inner end of the genital 

 slit. Under arm-plates squarish, small, 

 bounded without bv a slio-ht curve, within 

 and on the lateral sides by re-entering 

 curves ; outer corners projecting ; length to 

 breadth (eighth plate), 1 : 1.5 ; first plate 

 shaped like the segment of a circle, with 

 the curve outward, and having a little pro- 

 jection within, occupying the outer end of 

 mouth-slit ; towards the tip of the arm, the ophiozona imprpssa. (Lower side.) 



, , 1,1 "' geuital scales. 



plates are proportionately longer, but have 



the same general outline. Side arm-plates pretty large, and occupying 

 a good deal of upper and under surfaces of the arm, but not meeting 

 either above or below, even near its tip. Upper arm-plates broader 

 than long, broader without than within ; outer side slightly curved, 

 inner and lateral sides straight, outer corners cleanly rounded ; length 

 to breadth (seventh plate), 1:2; first two or three plates enclosed hy 

 notch in disk, and modified in breadth accordingly, short, thin, rudi- 

 mentary ; length to breadth of third plate, .6 : 1.8 ; towards tip of arm, 

 the plates are quadrangular, but with so short an inner side as to be 

 almost wedge-shape. In the centre of the disk, above, a rosette of six 

 separated, nearly circular primary plates, having a diameter of about 

 I"""- ; in each interbrachial space, above, five radiating rows of similar 

 separated plates or scales, the middle row being composed of four pri- 

 mary plates ; between all these are numerous little scales, having a 

 diameter usually of .S""', and arranged usually in single lines. Radial 

 shields pear-seed shaped, the point inward ; length to breadth, 2.2 : 1.4 ; 

 widely separated without by a triangle of three large round scales, and 

 within by a single lai'ge oval scale, between Avliich and the triangle are 



