304 A. M Verrill — North American Ophiuroidea. 



number and arrangement of the large angular plates outside the 

 oral shields are variable even on the same specimen. Usually there 

 are three or four of the larger j^lates, of which two stand side by- 

 side, near the margin of the disk. 



The radial shields are often separated distally by a row of two or 

 three small angular plates and a large proximal plate as in our figure 

 (pi. XLiii, fig. 1), but in other specimens the radial shields are in 

 contact distally, but separated ^jroximally by a single large triangu- 

 lar plate, as in Mr. Lyman's type-specimen of 0. nivea. The cen- 

 tral disk-plate is usually closely surrounded by five large angular 

 plates, but in many cases there are small plates intervening 'more or 

 less iri'egularly. The variations in the scaling of the disk and in 

 the radial shields are not coincident with the variations of the oral 

 shields. 



This species is allied to 0. tessellata. It is easily distinguished 

 by the large, irregular disk-plates, wide, oblong, oral shields ; three 

 subequal arm-spines, low down on the sides. There are no marginal 

 spinules outside the radial shields. The upper arm-plates also differ 

 in form. 



Off Havana, 110 to 263 fathoms (Bahama Exped.). Taken by the 

 Blake Exped. in 56 to 424 fathoms; off Barbadoes, 200 fath. (Blake 

 Exped.). 



Family, OPHIOTHRICHIDiE Ljung. 



Ophiothricidce Ljung., Opli. Viv., 1866. 



Ophiothrichidce Liitken, Addit., iii, 1869. Verrill, Bahama Exped., p. 18, 1899. 



Ophiothrichince Ljung., Joseph. Exp., 1871. 



The family is characterized b}'^ the well defined group of true 

 tooth-papillfe ; by the absence of oral papillfe ; hj the usually 

 numerous, long, slender, generally rough and glassy arm-spines; and 

 internall}^ by the complex, interlocking articulations of the arm- 

 bones, and the strong mouth-frames and large radial shields. The 

 peristomial plates, in the tjq^ical genera, are in three parts ; of these 

 the middle one is large, like an oral shield. The dental plate or 

 apical jaw-plate is a separate piece. 



This family, as now limited, includes the following genera : 

 Ophiothrix, Ophiothela, Opiiiocnemis, Ophio2)samniium, Ophiomaza, 

 Ophiogymna^ Ophiocampsis Duncan, Ophiotrichoides Ludw., Opliiop- 

 teron Ludw., Liitkenia Brock, Gymnolophus Brock, Ophiomthiops 

 Brock, Ophiosphmrea Brock, and Ophiolop/ius M. Tanner. 



