208 OPHIACTIS KRUYERL 



Ophiactis Krbyeri Lux ken. 



Ophincth Kroijcri Lutkk.v. Ylck'nsk. ModdoU'lscr. Jan., 1856. 

 Ophiactia Krotjeri Lutkex. Addit. ad Ili^t. Oph., p. 130. 



Sj)edal MarJcn. — Mouth-shields much broader than long, Avith a 

 peak within and a small tail without. Six (or five) arm-spines, all 

 smooth ; fourth (or third) from the top much the longest. 



Description of a SiJecimen. — Diameter of disk, 5""°' ; from outer 

 side of mouth-shields to outer corner of opposite mouth-slit, 2.5"""' ; 

 width of arm without spines, 1.5"""- ; length of arm about 25™""- ; dis- 

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

 between outer corners of mouth-slits, .9 : 1.4. Mouth-papillae, two to 

 each angle of jaw, thin, wider than long, with a bevelled, cutting edge. 

 Teeth nine, short, thick, stout, and crowded ; third and fourth from 

 below broadest ; uppermost one smallest and narrowest. Mouth-shields 

 much broader than long, with a little tail or peak without, and a 

 rounded peak within ; lateral corners rounded ; length to breadth, 

 .5 : .9. Side mouth-shields small, narrow, irregularly triangular, not 

 meeting within ; they are unusually variable in size and shape. Under 

 arm-plates without sharp angles, broader than long, outer side and cor- 

 ners curved, lateral sides nearly straight, inner side strongly curved, 

 forming sometimes a rounded angle ; first plate short and very small, 

 often separated from second plate by side mouth-shields ; next three or 

 four plates smaller than those immediately beyond ; length to Ijreadth 

 (eighth plate); .6 : 1. Side arm-plates projecting strongly, encroaching 

 a little below. Upper arm-plates a good deal broader than long, squar- 

 ish ; outer and lateral sides nearly straight, inner side slightly curved ; 

 corners a little rounded ; length to breadth (twelfth plate), .6:1; the 

 first two or three plates are smaller and oval. Disk-scales much crowded, 

 varying somewhat in length, but of nearly the same size ; al^out 12 to 

 a square imn. ; in the middle is a single primary plate, and there is a 

 connected, radiating row, of three or four plates, in each interbrachial 

 space ; along margin of disk, a good number of small, stout, conical 

 spines, about .3""°' long ; there are a few others scattered on upper sur- 

 face of disk, and some on the interbrachial spaces Ijelow. Radial shields 

 swollen, long triangular, with their points inward ; where they are 

 joined, without, there is a slight lobe ; for the rest of their length they 

 are separated by a stout wedge of one, two, or three scales ; length to 

 breadth, 1.5 : .8. Arm-spines, near base of arm, six, very smooth, 

 rounded, hardly tapering, blunt and rounded at the point ; uppermost 

 and lowest spines shortest, fourth from the top the longest, others inter- 



