10 Ol'IIIOTlIKLA TIGRIS. 



full width iit the 7th or 8th plate ; disk naked below and covered by 

 thick, wrinkled .skin ; radial shields very large, pear-seed shape, length, 

 to breadth, 4 : 2.5, separated by a band of three or four elongated, 

 narrow, broken, and irregular plates, which come to the edge of tlie 

 disk, and are continuous with the iipper arm-plates. Interbrachial 

 spaces covered by plates similar in form to those between radial-shields, 

 but wider ; in the centre, a rosette of small, very irregular pieces, one 

 in the middle, and five close around it. The edge of the disk has a 

 row of stout, swollen plates, three to five in each interbrachial space, 

 of which one is opposite the radial-shield on either side, and from one 

 to three are opposite the interbrachial plates. Arm-spines usuallj^ five 

 sometimes six ; the two or three upper ones much the longest ; all 

 stout, tapering, blunt, cylindrical; lengths, to that of the upper arm- 

 plate (7th joint), 2.2,2, 1.0, 1, 1, .5 : .9. Near end of arm, three or 

 four spines, of which the nnder one is much swollen at the base, and 

 slightly hooked at the end. Color, in alcohol : deep chocolate. Zan- 

 zibar, collected by Mr. Cooke. 



Ophiothela tigris. Si-, xov. 



Plate 1., figs. 10, 11. 12. 



Special Marks. — Back of disk completely covered hy the radial- 

 shields, which are quite smooth, as are also the interbrachial spaces 

 below. Five arms. 



Description of a Specimen. — Diameter of di.sk, 7"""' ; lengfii of arm 

 (which had been I'epaired), 12""" ; fiom outer corner of moulh-slit to 

 outer edge of opposite mouth-shield, S"'"'" ; widtli of arm, includmg side 

 arm-plates, 2""" ; distance from outer corner of mouth-sliicld to points 

 of tooth-papillai, to that between outer corners of mouth-slits, l.G : l.o. 

 Tooth-papilliB arranged in a close, vertical, oval clump ; about fifteen in 

 number; four stout, flattened, squarish teeth, whicli with the tooth- 

 papilla? form a dentition like that in Ophiothrix (a generic character) ; 

 mouth-shields irregular, sometimes in form only of a small swelling ; 

 but, when cleai'ly defined, having an oval heart-shape, with outer side 

 straight, and with length to breadth, .-5 : 1. Side mouth-shields large 

 and conspicuous ; their free lateral sides re-enteringly curved ; their 

 inner latarals joined along their whole length; their inner sides making 

 together a wide curve ; under arm-plates covered with thick skin and 

 seen indistinctly, except when dry. They have an iri'egular triangular 

 form, with a peak within and a lumpy surface. They cover only a part 

 of the arm, and differ in figure one from another. Side arm-plates 



