330 BULL''. I IX OF THE 



irregular, overlapping scales, of which there are five or six in a line from 

 the centre to the margin of the disk. These scales are beset with numerous 

 bodies of two sorts; the first are short, stout, rough spines, similar in size 

 and shape to the mouth-papillae ; the second are shorter but much thicker 

 and have a thickened club form. In the interbrachial spaces below these 

 spines are more scattered. Over each arm the outer points of the radial 

 shields can just be seen ; the rest is covered. Five rough, rounded, tapering, 

 rather stout arm-spines; lengths to that of the under arm-plate (4th joint) 

 1.7, 1 .5, .8, .7, .G : .3. Towards the end of the arm there still are five spines, 

 and the two upper ones much the longest. Tentacle scales, one to each 

 pore ; on the first two pairs of pores long, flat, and spine-like, resembling the 

 mouth-papilla; ; on the joints beyond, smaller and proportionately shorter. 



Color, in alcohol, light bfown. 



Variations. — The two specimens from 125 fathoms had no spines on the 

 disk, and only a few of the club-shaped grains. 



In 125 and 324 fathoms. 



This species, with 0. clavigera Ljung., stands at one extremity of the genus 

 and approaches Ophiacanlha just as 0. Krebsii, at the other extremity, tends 

 towards Amphiura. The typical Ophiactis of Liitken is distinguished by 

 great radial shields, fiat arms, stumpy arm-spines, and feebly developed 

 mouth-frames ; its scaling is heavy, and the arm-plates are large and con- 

 spicuous; and, as such, it was set off from Amphiura. Ophiacantha is dis- 

 tinguished by the development of thorny appendages on the disk, which 

 cover it closely ; feeble upper and lower arm-plates ; long, rough arm- 

 spines ; a stout chewing apparatus, which is somewhat like that of Ophiocoma, 

 except the absence, of tooth-papilla;; and very slender linear radial shields 

 covered with skin. 



O. clavigera is remarkable for its high arched disk. 



Ophiactis plana Lyman, sp. nov. 



Special Marls. — Disk scales smooth, without spines or grains. Four 

 mouth-papilla; to each angle. Side mouth-shields touching the under arm- 

 plate. 



I> cription of a Specimen. — Diameter of disk 3.5 mm. Length of arm 

 10 mm. Mouth-papillae,* two to each angle, situated at the outer corner 



* I' has been explained (see remarks on Amphiura) that this papilla is really the 

 cle scale of tl pair of mouth tentacles. In describing Ophiactis there has 



been some confusion in this re pect: thus, Mr. Ljungman says of 0. carnea, " papillae 

 binaj " ifour to each angle), "alteram sum mo sinu orali collocata"; but this 

 tentacle scale of the first pair of mouth-tentacles; and at that rate the 

 - usually described as having lour papillce to each mouth-angle ought to he reck- 

 as having six, because these tentacle scales of the first pair arc commonly over- 



