﻿OPIIIACTIS. 105 



OPHIACTIS LiJTKEN. 



Type of the Genus, 0. Krebsii. 



Disk circular, robust, closely covered with radial shields and overlap- 

 ping scales, the latter bearing a greater or less number of small spines. 

 Teeth. No tooth-papillte. A few (usually two or four) small, delicate 

 mouth-papillaj to each angle of the mouth, situated near the outer cor- 

 ner of the mouth-slit. Arm-spines arranged along the sides of the side 

 arm-plates. Two genital slits beginning outside the mouth-shields. 



GKODPING OF SPECIES HEREIN DESCHIBED. 



Radial shields separated and "j 

 very small ; side mouth- 

 shields broad, and making > 0. simplex. 

 a continuous ring round 

 the mouth, J 



Five arms in the adult, Two mouth-papillaj, -j Mouth-shields much broad- "1 



er than long ; arm-spines I ^ r,-.. 

 smooth, tapering, differing f 

 much in length, J 



Arm-ppines very short, blunt, ] ^_ Miilkn. 

 rough ; nearly equal, j 



f A slight lobe on the outer '\ 0. Krebsii. 

 Six arms in the adult. Four mouth-papilla?, < side of the upper arm- |- 0. virescens. 



( plate, ) 0. sexradia. 



Ophiactis simplex Lutken. 



OpMolepis simplex Le Conte. Proceed. Phil. Acad., V. p. 318. Nov., 1851. 

 Ophiactis (Opkiolepis) simplex I^utken. Addit. ad Hist. Oph., p. 130. 

 Ophiactis Orsledii? LOtken. Addit. ad Hist. Oph., p. 129. 

 Ophiactis arenosa? Lutken. Addit. ad Hist, Oph., p. 129. 



Special Harks. — Radial shields widely separated, and comparatively 

 small ; spines very numerous in the lower interbrachial spaces ; disk- 

 scales inchning to a circular form, rather regular. 



Description of a Spiecimen. — Diameter of disk, i""- ; from outer side 

 of mouth-shield to outer corner of opposite mouth-slit, 1.7°""" ; width of 

 arm without spines, l.l""- ; length of arm about 28°"°- ; distance from 



