206 



BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



arm plates near middle of arm are also a good character. On the 

 whole the nearest ally of anchilabra is Koehler's species vorax, from 

 which it seems to differ only in the smooth arm spines and in the 

 absence of bare scales and radial shields at the bases of the arms. 



OPHIACANTHA TRACHYBACTRA, new species.^ 



Disk 12 mm. in diameter; arms about 60 mm. long. Disk covered 

 by numerous, nearly cylindrical stumps, crowned with several minute 

 spinules. Radial shields concealed, but in dry specimens their form 

 and position is clearly indicated by long, narrow, well-separated 



ridges. . Arms rather 

 stout; upper arm 

 plates rounded tri- 

 angular, about as wide 

 as long, well sepa- 

 rated; the side arm 

 plates, however, do 

 not in the type meet 

 on basal part of arm ; 

 in smaller specimens 

 they do. Interbra- 

 chial spaces below 

 well covered with 

 more or less pointed 

 stumps. Genital slits 

 small. Oral shield 

 small, somewhat pen- 

 tagonal, quite varia- 

 ble in proportion of 

 length and breadth; 

 c o m m only much 

 wider than long. 

 Adoral plates very 

 large, wide, and thick, 

 meeting broadly with- 

 in. Oral papillae nu- 

 merous, five or six on a side, besides one at apex of jaw, subequal, 

 long, thick, bluntly pointed. First under arm plate rather large, some- 

 what hexagonal, wider proximally than distally; succeeding plates 

 ranging from nearly triangular to nearly square; wider than long, 

 widely separated. Side arm plates large, separating the upper arm 

 plates above (even if they do not quite meet each other) and meeting 

 broadly below; each plate carries six or seven rather thick arm spines, 



a Tpa^ug, signifying rough, and ^oKxpov, signifying cluh, in reference to the rough, 

 club-shaped, lower arm spines. 



Fig. 96. — Ophiacantha trachybactka. x 4. a, from above; 6, 

 FROM below; c, side view of two arm joints near disk. 



