14 



THE VOYAGE OF H.M.S. CHALLENGER. 



plate just outside the true mouth shield. Two genital openings in each interbrachial space- 

 Pectinura is separated from Opliiopeza only by having a supplementary plate outside 

 the mouth shield ; and both are distinguished from Ophiura by the minor anatomical char- 

 acter in this last, that, by a partial adhesion of the edges of the genital openings, each one 

 is divided into two. The similarity actually found in the skeletons would be expected. In 

 all three the disk is enclosed by a coat of stout imbricated scales and strong radial shields. 

 The genital plates, thick and rather wide, are attached to short, stout genital scales, 

 which, in Ophiopeza and Pectinura are articulated farther inward, thus shortening the 

 genital opening. The mouth frames and jaws are strong and finely curved and bear three 

 thick peristomial pieces whereof two form an angle, whose opening outward is wedged by 

 the third. The arm bones are of a high type, having thin wings, and the umbo, articu- 

 lating peg and other subordinate parts well marked. 



Disk cov- 

 ered, under 

 its granula- 

 tion, with 

 coarse scales 

 or swollen 

 plates. 



Disk, under 

 its granula- 

 tion, cover- 

 ed with, 

 minute and 

 smooth 

 scales. 



No pores between 

 under arm plates, 



Table of Species of Pectinura. 



Radial shields granulated. 13-15 arm spines, 

 Radial shields granulated. 9 short arm spines, 



Pores between first 

 and second under 

 arm plates, 



Ten thin equal arm 

 spines ; underarm 

 plates encroached 

 on by side arm 

 plates, . 



Pores only between 

 first and second 

 under arm plates, 



Pores between the 

 under ami plates 

 continued for 

 some distance 

 along the arm, . 



Of doubtful place, 



Radial shields naked ; also some other disk 

 plates. 9 arm spines, 



. Radial shields naked. 3 arm spines, . 



' Arms cylindrical at their insertion in the disk, 

 which is puffed, .... 



Arms widened at their in- \ 10-11 arm spines, 

 sertion in the disk, which > 

 is flat, . . ) 5-6 arm spines, . 



Pectinura qrinosa. 

 Pectinura arenosa. 



> Pectinura inferncdis. 

 Pectinura h&ros. 



> Pectinura gorgonia. 



Pectinura marmorata. 

 Pectinura dellata. 



7-8 conical arm spines, the lowest one a little 

 the longest, .... 



8-9 flat, pointed arm spines, the lowest one 

 very long and flat, often equal to two joints 

 in length, ..... 



Pectinura vestita. 



Pectinura maculafa. 



> Pectinura septemxpi nosa. 



Pectinura rigida. 

 Pectinura verrucosa. 



