MONOGRAPH OF JAPANESE OPHIUROIDEA. 125 



serrate, the lowest one being hook-shaped in distal arm 



joints ; ventral arm plates large, wide, nearly as wide as the 



corresponding arm joint ; genital bursae well developed ; 



genital plates, genital scales, generative glands and peristomial 



plates unknown, but probably normal ; distal vertebrae 



unknown. 



In view of these differences, the two groups can hardly be 



united in a single genus. I therefore propose the name Ophiuro- 



thamnus, nov., for the so-called Ophiofhamnus, to distinguish it 



fi'om the genuine Ophiotfiamnus. 



There are two other species, viz. Ophiothamnus gracilis Studer, 

 (1882) 1883, and Ophiacantha gracilis Vereill, 1885 (referred to 

 Ophiothamnus by V., 1899), which have been referred to Ophiothamnus, 

 but probably belong neither to the genuine Ophiothamnus nor to 

 Ophiurothamnus. Though I am not able to settle their systema- 

 tic position owing to their very imperfect descriptions, they may 

 possibly be referable to Ophiacantha. 



Ophiothamnus Lyman, 1869, emend. 

 Sjn. OpMoleda Kœhler, 1906. 



Disk divided into five brachial lobes, covered with fine, 

 imbricating scales, and beset with scattered spines. Eadial shields 

 large, naked, more or less joined in pairs outwards. Genital 

 bursœ very rudimentary, being represented by the creases between 

 the disk and the arm bases. Oral shields small, separated by the 

 large adorai shields from the first lateral arm plates. Three or 

 four oral papilla3 on either side of each jaw, the outermost one 

 being very large and operculiform. Peristomial plates very large, 

 triple. Arms inserted ventrally to the disk, composed of long, 

 slender, hour-glass-shaped joints. Arm spines long, slender, spini- 



