138 HEMIPIIOLIS CORDIFERA. 



of arm without spines, l.T""™"; length of arm, 81™°-; distance from outer 

 side of mouth-shields to inner points of teeth, to that between outer 

 corners of mouth-slits, 1.6 : 1.8. Mouth-papilla3 small, flattened, rounded, 

 situated at the very base of the jaw-frames. Teeth nine, blunt, squarish, 

 much thickened at the middle point of their cutting edge ; uppermost 

 one sharp, and much longer than the rest ; lowest one projecting less 

 inward than the others. Mouth-shields irregular oval, more strongly- 

 curved without ; lenii-th to breadth, .6 : .9. Side mouth-shields lono;, 

 narrow, meeting within. Under arm-plates regular, jjroader than long, 

 with rounded corners, so as to be nearly oval ; length to breadth 

 (twenty-fourth plate), .6 : 1. As the side mouth-shields meet on the 

 middle line of the arm, the first under arm-plate is reduced to a little 

 papilla at the outer corner of the mouth-slit. Side arm-plates small, 

 with but a small ridge ; encroaching slightly on upper arm-plates. 

 Upj)er arm-plates much l^roader than long, outer side nearly straight, 

 and broader than the inner ; lateral corners ending in a rounded point ; 

 length to breadth (twelfth plate), .6 : 1.5 ; the first two or three plates 

 are enclosed by the notch in the disk, and are rudimentar}^ Scales of 

 disk small, rather thick, more or less rounded ; among them may be 

 distinguished the primary plates ; on the middle line of each interbra- 

 chial space is a raised, radiating row of scales, each overlapped by its 

 predecessor, but with its other edges free ; on either side of this row 

 the scales are smaller, and overlap each other like those of a fish. 

 Kadial shields pear-seed shaped, with the point inward ; large ; length 

 to breadth, 1.9 : 1.2 ; set back a little from the margin of the disk, sepa- 

 rated by a wedge of three scales, whereof the outer is long and narrow, 

 the inner nearly round, and the middle one intermediate ; on each side 

 of the notches in the disk, three or four little, slender papilla), like 

 small arm-spines. The scaly coat extends over the disk margin, and 

 there ceases abruptly. Under surfiice covered with a naked, somewliat 

 wrinkled skin ; along edges of genital slits a row of small, tapering, 

 fleshy papilla?. Arm-spines equal, rounded, tapeiing, sharp ; lengths to 

 that of under arm-plate, .7, .7, .7 : .6. Tentacle-scale one, small, flat, a 

 little longer than broad, rounded, standing well clear of lower arm-jDlate. 

 Color, in alcohol : above, ground color greenish gray (sap-green and 

 neutral tint), radial shields and some of the disk-scales much lighter ; 

 arms rather darker than disk, growing lighter towards their tips, but 

 banded with dark rings, each including one or two joints ; below, inter- 

 brachial spaces brownish flesh-color ; under arm-plates same color as 

 U23per surface, but much paler -, arm-spines nearly white. 



Variations. — According to Professor Agassiz's colored drawings, the 

 tints vary very much ; the ground color of the disk may be dull indigo- 

 blue, various shades of greenish, yellowish brown, yellow, gray, or 



