276 



BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



Type-species . OpTiiosyzygus disacanthus. 



Although this genus is doubtless rather nearly related to OpTiiocy- 

 nodus, the disk structure being essentially the same in the two, the 

 difference in mouth parts is too marked to allow them to be united, 

 even if the remarkable web on the arm. spines of Ophiosyzygus be 

 ignored. 



OPHIOSYZYGUS DISACANTHUS, new species, a 



Disk 16 mm. in diameter; arms about 60 mm. long probably. 

 Disk covered with an apparently naked skin, which under a micro- 

 scope is seen to contain numerous thin scales, and bears scattered 

 calcareous granules. Radial shields wanting, but expanded ends of 

 genital plates are conspicuous through skin at base of each arm. 

 Upper arm plates wanting. Interbrachial spaces below naked. 

 Genital slits small. Oral shields small, about as long as wide. Adoral 



FIG. 139. OPHIOSYZYGUS DISACANTHUS. X 3. a, FROM ABOVE; 6, FROM BELOW; c, SIDE VIEW OF TWO 



ARM JOINTS NEAR DISK. 



plates large, much wider without than within where they meet. 

 Oral papillae, about three on a side, at distal end of mouth slit, small, 

 almost conical, acute. Teeth (tooth papillae ?) few, irregular in num- 

 ber, size, and position, spiniform with rough tips, clustered at apex of 

 j aw. Under arm plates longer than wide, somewhat tetragonal, 

 distinct at base of arm, but quickly becoming very thin and indistinct, 

 especially proximally. Side arm plates low but becoming very long 

 distally, each bearing on its swollen, distal end, two spines, of which 

 upper equals (at base of arm) two joints and lower is distinctly 

 shorter; spines, slender, acute. Upper spine on each joint connected 

 with adjoining upper spines by a thin, broad, horizontal membrane, 



dlf, signifying twice and 

 of arm spines. 



signifying spine, in reference to the number 



