142 OPHIONEREIS RETICULATA. 



approach the hexagonal form ; the inner side and inner laterals become 

 distinct from each other, as do the outer side and outer laterals. Close 

 to tip, length to breadth, .4 : .8 ; at tip of arm, plates heart-shaped, the 

 point inward. Supplementary upper plates fill the space between true 

 upper arm-plates and upper arm-spine ; they are nearly triangular, with 

 two angles directed sideways, and one inward ; side next upper arm- 

 plate, nearly straight ; other two a little curved ; length of sides at 

 tenth joint, outer side 1, other two .8. Disk : radial shields small and 

 narrow, blunt at outer end, sharp at inner end, placed just opposite out- 

 side line of each arm ; length about I"""' ; breadth, .4"'"' ; starting from 

 each radial shield, and running along edge of disk, is a row of about 

 seven scales, much larger than the rest, largest having a length of .4'"'°' ; 

 scales just round and between radial shields somewhat larger than those 

 toward centre of disk, which are very minute, about 230 to a square mm.', 

 on under surface of disk, similar scales ; starting at mouth-shield, and 

 running along edge of genital slit for about half its length, is a narrow 

 ridge, bearing a single row of small papillag. Arm-spines : second joint, 

 two ; length to that of under arm-plate, .6, ,6 : .6 ; third joint, three 

 spines ; fourth joint, three spines, .6, .8, .8 : .6 ; seventh joint, three 

 spines, .8, 1.2, .8 : .6 ; all other joints, to very near tip of arm, three 

 spines ; twenty-second joint, 1.2, 1.6, 1,4 : .8 ; about two thirds out on 

 arm, ,8, 1, .8 : .8 ; it is only at extreme tip of arm that there are only 

 two spines. Tentacle-scales near base of arm having a length of .4™"", 

 in form short oval. Color, in alcohol : general tint of upper parts very 

 light grayish-brown (vandyke-brown and a little neutral tint) ; upj^er 

 surface of disk irregularly reticulated with lines of light brown ; upper 

 surface of arms barred with greenish black ; bars usually the width of 

 a joint, seldom more ; their dark color not uniform, but concentrated 

 round edges of upper arm-plates ; general tint of under surface like that 

 of upper, but lighter ; mouth-shields, tentacle-scales, larger arm-spines, 

 and some of under arm-plates, faintly marked with light brown ; towards 

 end of arm some faint bars on its under surface ; just outside mouth- 

 shield, the interbrachial space is dark umber-brown. 



Variations. — A young one, with a disk of 3™"', differed from the 

 adult principally as follows : the disk had the primary plates still 

 large and distinct, although they were smaller, and the other scales 

 more numerous than in the young 0. anmdata of the same size ; the 

 under arm-plates were longer ; the mouth-shields were pointed at their 

 inner end, and the side mouth-shields were so large as nearly, or quite, 

 to meet within. The proportions of the disk to the arms range as fol- 

 lows : 5.1 : 23, 8 : 47, 10 : GO, 11.5 : 90. The colors vary but little. 



This species is distinguished fiom O. anmdata by having the middle 

 arm-spine shorter ; from O. porrecta, by longer arm-spines ; and from 

 O. Xantusii, by sharper arm-spines and longer arms. 



